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Worksheetsmodule 5 lesson 2 friction
Total questions: 150
Worksheet time: 1hrs 15mins
Which statement best defines friction in mechanics?
Energy created when objects accelerate quickly
Force causing uniform circular motion of objects
Momentum gained when surfaces move together
Force opposing relative motion of surfaces
A book rests on a table. Which friction acts just before the book starts sliding when you push gently?
Kinetic friction during constant speed
Fluid friction from surrounding air
Static friction at the contact surface
Rolling friction from the table legs
When a sled moves across ice, which friction type primarily resists its motion?
Rolling friction inside the sled runners
Kinetic friction between sled and ice
Magnetic friction due to Earth’s field
Static friction locking sled to ice
Which change most likely decreases friction between two solid surfaces?
Increasing normal force pressing surfaces
Adding a lubricant layer between surfaces
Increasing contact area with stronger clamps
Making surfaces rough with coarse grit
The frictional force is often modeled as f = μN. What does μ represent?
Coefficient of friction for contacting materials
Mass density of the moving object
Potential energy stored in the surface
Mechanical advantage of applied lever
A cart of mass 10 kg experiences a kinetic friction force of 15 N while pulled on level ground. What is the approximate coefficient of kinetic friction if the normal force is 98 N?
μk ≈ 9.8 from mass times gravity
μk ≈ 0.02 from dividing N by f
μk ≈ 6.5 using f·N relation
μk ≈ 0.15 from f/N calculation
Why do racing tires have slick surfaces rather than deep tread on dry tracks?
Increase contact adhesion and static friction
Reduce mass to lower gravitational force
Allow more air flow to cool the brakes
Decrease normal force during cornering
A block requires 20 N to start moving but only 14 N to keep moving at constant speed. What does this indicate about friction?
Both frictions are exactly identical
Kinetic friction exceeds static friction
Static friction exceeds kinetic friction
Friction disappears after motion begins
Which situation best illustrates useful friction?
Walking without slipping on a sidewalk
Metal gears overheated by rough contact
Ship slowed excessively by water drag
Skier losing speed on sticky snow
On an inclined plane, a block remains at rest. Which factor most directly explains this?
Kinetic friction cancels all net forces
Static friction balances downhill component
Normal force equals gravitational weight
Air resistance increases upward motion
What is friction best described as in physics?
A pressure that increases contact
A push that speeds objects up
A force that opposes motion
A pull that aligns surfaces
When a book slides across a desk and you stop pushing, why does it slow down?
Friction acts opposite motion
Gravity reduces horizontal speed
Normal force pulls the book back
Air pressure increases surface grip
Which statement about surfaces explains why friction occurs?
No surface is perfectly smooth
All surfaces are ideally rigid
Smooth surfaces never touch
Microscopic contact is negligible
At the microscopic level, what causes friction between contacting surfaces?
Perfectly flat planes slide freely
Electrons stop moving entirely
Gravity compresses materials uniformly
Irregularities interlock during contact
Which direction does friction act relative to an object's motion?
Opposite the direction of motion
In the same direction as motion
Randomly without orientation
Perpendicular to the motion
If you push a book harder on the same desk, what immediate effect does friction have while it is sliding?
It still opposes motion
It begins to assist motion
It becomes zero instantly
It reverses direction unpredictably
Which scenario most clearly demonstrates friction?
A ball floating in water
A planet orbiting the sun
A hockey puck slowing on ice
A magnet attracting iron
Why does a stationary book not start sliding by itself on a level desk?
Air pushes it forward gently
Gravity cancels all forces
Static friction resists initial motion
The desk provides net acceleration
Which claim about friction is incorrect based on the material?
Friction is a contact force
Friction can stop moving objects
Friction arises from surface roughness
Friction acts to increase motion
When surfaces appear smooth to the eye, what is still true about them?
They have microscopic irregularities
They are perfectly flat and featureless
They remain frictionless under pressure
They cannot produce friction at all
Which statement best identifies the two main types of friction shown in the slide?
Static friction and kinetic friction
Rolling friction and fluid friction
Viscous friction and air resistance
Magnetic friction and elastic friction
Static friction primarily acts when which situation is true?
A fluid flows around a solid object
An object remains at rest on a surface
Wheels rotate without slipping on ice
Surfaces move steadily past each other
Kinetic friction is most directly involved when a box is pushed and it slides across the floor. What is the best description?
Force causing objects to stick together
Force increasing speed during sliding
Force opposing motion while sliding
Force resisting start of motion
Which pair correctly matches the friction type with typical motion state?
Static friction — constant-speed sliding
Kinetic friction — object at complete rest
Kinetic friction — object anchored to surface
Static friction — object not yet moving
A student slowly increases the pushing force on a heavy crate. Before it begins to move, which friction type mainly balances the push?
Fluid friction acts due to air flow
Static friction acts while at rest
Rolling friction acts due to wheels
Kinetic friction acts during sliding
After the crate starts moving, which friction type becomes dominant as it continues to slide?
Viscous friction only in liquids
Elastic friction storing potential energy
Static friction opposing motion at rest
Kinetic friction opposing motion while moving
Which scenario best illustrates static friction?
Block sliding down a rough ramp
Car tires gripping road before rolling
Skier gliding down a snowy slope
Boat moving through calm water
Which scenario best illustrates kinetic friction?
Nail embedded and unmoving in wood
Book resting on a table top
Magnet stuck to a refrigerator
Sled sliding across packed snow
Why is the maximum static friction typically greater than kinetic friction for the same surfaces?
Sliding reduces microscopic contact locking
Air pressure becomes dominant during sliding
Resting decreases normal force on surfaces
Moving increases surface temperature drastically
If static friction prevents motion until a threshold force, what happens immediately after the threshold is exceeded?
Kinetic friction takes over during sliding
No friction acts on the object anymore
Normal force becomes equal to zero
Static friction becomes infinite instantly
Which statement best defines static friction?
Force acting only when objects are moving fast
Force that accelerates objects on rough surfaces
Force exerted by a surface with no relative motion
Force opposing motion when surfaces slide
You push a heavy couch and it does not move. What force primarily prevents motion?
Normal force from the floor
Static friction between couch and floor
Air resistance around the couch
Kinetic friction between couch and floor
Static friction acts when two surfaces have what condition?
No relative motion between surfaces
Increasing acceleration between surfaces
High temperature in both surfaces
Constant velocity between surfaces
Which scenario most likely involves static friction rather than kinetic friction?
Ice skater gliding across the rink
Sliding a book across a desk steadily
A ball rolling down a ramp smoothly
Trying to start moving a stuck box
Which change would most likely overcome static friction to start motion?
Reduce the applied force slightly
Increase air resistance significantly
Increase the applied force beyond a threshold
Decrease the normal force to zero
A student pushes a crate with 120 N, and it remains at rest. What can be inferred about static friction magnitude?
It can be up to 120 N opposing push
It is greater than 120 N exactly
It is less than 120 N exactly
It equals the normal force always
Which description fits the example given for static friction?
Pulling a sled that slides on snow
Pushing a couch and it does not move
Pushing a couch and it moves slowly
Kicking a ball that starts rolling
Why does static friction matter when starting motion of an object at rest?
It removes the normal force completely
It reduces mass of the object
It provides energy to the object
It balances small applied forces initially
When static friction is acting, the object’s state of motion is best described as
At rest relative to the surface
Moving at constant speed
Accelerating forward quickly
Oscillating back and forth
Which statement distinguishes static friction from kinetic friction?
Static only appears with very smooth surfaces
Static occurs before motion begins
Static occurs during sliding motion
Static only acts in the direction of motion
Which statement best describes when static friction acts on an object at rest?
It acts only if the surface is perfectly smooth
It acts only after the object starts moving
It acts only when an external force is applied
It acts continuously without any external force
Static friction adjusts its magnitude to match the applied force. What constraint limits this adjustment?
It is limited by object mass only
It is limited by surface temperature
It is limited by a maximum threshold
It has no upper limit in magnitude
In which direction does static friction act relative to the applied force trying to move the object?
At a random angle to the applied force
Perpendicular to the applied force
Opposite direction to the applied force
Same direction as the applied force
What is the value of static friction when no external force attempts to move the object?
It is a small constant value
It is equal to zero
It equals the object’s weight
It equals the normal reaction
A student gently pushes a box with a 3 N force, and the box remains at rest. Which statement explains this outcome?
Static friction is exactly 3 N
Static friction is less than 3 N
Static friction does not act at all
Static friction is greater than 3 N
Which scenario demonstrates static friction reaching its maximum limit?
A crate accelerates under a tiny push
A crate begins sliding after a stronger push
A crate moves steadily without any push
A crate remains at rest under any push
If the maximum static friction between a block and floor is 10 N, what happens when a 8 N horizontal force is applied?
The block rotates about its edge
The block remains at rest
The block moves at constant speed
The block accelerates immediately
Which change would most likely increase the maximum static friction between two surfaces?
Cooling the surfaces slightly
Increasing normal force between surfaces
Polishing surfaces to be smoother
Reducing normal force between surfaces
A 12 N push is applied, and the object just starts moving. If the maximum static friction was 11 N, which statement is correct?
Static friction exceeded 12 N before motion
Static friction matched 12 N during motion
Static friction was zero before motion
Static friction peaked at 11 N before sliding
When a small horizontal force is applied to a resting book, what does static friction do as the force increases gradually?
Increases to match up to a limit
Decreases as the force increases
Instantly exceeds the applied force
Remains constant until sliding occurs
What happens when the applied force exceeds the maximum static friction on an object?
The coefficient of friction increases
The normal force becomes zero
The object starts moving forward
The object stays perfectly at rest
Which term replaces static friction once the object begins to move?
Elastic restoring friction
Viscous drag friction
Kinetic (sliding) friction
Rolling resistance friction
Which quantity is dimensionless in the maximum static friction relation?
Maximum static friction force
Normal force on the surface
Applied pushing force
Coefficient of static friction
Choose the best description of maximum static friction.
The friction that acts only during motion
A force always larger than kinetic friction
The greatest static friction before motion
A fixed value independent of surfaces
If the normal force on a block doubles, how does the maximum static friction change (same surfaces)?
It becomes four times larger
It becomes half as large
It stays exactly the same
It doubles in magnitude
A crate remains at rest when pulled with 80 N but starts sliding at 82 N. What is the best estimate of its maximum static friction?
About 80 newtons
About 100 newtons
About 120 newtons
About 60 newtons
Which statement correctly compares static and kinetic friction for the same surfaces?
Both are always exactly equal
Neither depends on the normal force
Kinetic is usually larger than static
Static is usually larger than kinetic
Identify the symbol typically associated with the normal force in friction formulas.
Lowercase f symbol
Capital N symbol
Lowercase a symbol
mu sub k symbol
When analyzing impending motion, which force balance condition is most relevant just before sliding begins?
Net force equals maximum static friction
Net force equals zero at threshold
Applied force equals normal force
Kinetic friction equals applied force
A 10 kg box is on a level floor. Take g = 9.8 m/s^2 and coefficient of static friction μs = 0.4. What is the maximum static friction?
About 392.0 newtons
About 98.0 newtons
About 39.2 newtons
About 19.6 newtons
Which situation best illustrates kinetic friction?
A balloon sticking to a wall after rubbing
A box resting on the floor unmoving
A book sliding across a desk surface
A magnet attracting paper clips upward
Kinetic friction acts when which condition is met?
Two surfaces are separated by air gaps
Two surfaces are pressed without motion
Two surfaces are perfectly smooth and cold
Two surfaces are sliding past each other
What is the main difference between kinetic and static friction?
Static increases with higher speeds
Static acts only with liquids present
Kinetic depends on object mass only
Kinetic occurs during sliding motion
A 2 kg book is pushed so it slides at constant speed. Which statement is true about forces along the desk?
Push equals kinetic friction force
Push is greater than kinetic friction force
Push is less than kinetic friction force
No friction acts on the sliding book
If the same book slides on a rougher desk, what changes most directly?
Mass of the book in kilograms
Normal force due to Earth’s pull
Magnitude of kinetic friction force
Direction of gravitational force
Which factor primarily determines kinetic friction between two surfaces?
Color and shape of the object
Temperature of the surrounding air
Volume of the sliding object
Nature of surfaces and normal force
While a book slides right across a desk, the kinetic friction force points in which direction?
Downward into the desk
Left opposite the motion
Right along the motion
Upward away from desk
A student claims kinetic friction acts only when speeds are high. What is the best evaluation of this claim?
Correct, only above a threshold speed
Correct, only above ten meters per second
Incorrect, it acts at any sliding speed
Incorrect, it acts only when resting
Which example would NOT involve kinetic friction?
A crate skidding to a stop on floor
A sled gliding downhill on snow
A book held still on a tilted desk
Shoes sliding across ice while moving
When a book slides and slows down on a desk, what energy conversion is most reasonable?
Chemical energy to gravitational energy
Kinetic energy to thermal energy
Potential energy to electrical energy
Thermal energy to kinetic energy
Which statement best describes when kinetic friction acts on an object?
Both at rest and moving equally
Only while the object is moving
Only while the object is at rest
Only when a force is removed
Compared to maximum static friction, kinetic friction is generally:
Larger in magnitude for all surfaces
Zero unless surfaces are rough
Smaller in magnitude on similar surfaces
Equal in magnitude in every case
What is the typical behavior of the magnitude of kinetic friction during motion?
Nearly constant for a given surface
Rapidly increasing with speed
Always decreasing to zero
Randomly fluctuating each moment
In which direction does kinetic friction act relative to an object's motion?
At a random angle to the motion
Same direction as the motion
Opposite the direction of motion
Perpendicular to the motion
A box slides across a floor at constant speed. Which statement is most accurate?
Kinetic friction accelerates the box forward
No friction acts on the box
Static friction balances the applied force
Kinetic friction balances the applied force
A student claims kinetic friction acts even before motion begins. Choose the best evaluation.
Incorrect; friction never acts
Correct only on smooth surfaces
Correct; friction always acts
Incorrect; that is static friction
Which change is most likely when a stationary block just starts sliding?
Friction drops from maximum static to kinetic
Friction rises from kinetic to larger static
Friction remains exactly the same
Friction becomes zero immediately
A sled moves to the right on snow. Which arrow shows the kinetic friction on the sled?
Upward, normal to the surface
Downward, due to gravity
Rightward, along the motion
Leftward, opposite the motion
During steady sliding on a level surface, which pair of forces is most relevant for horizontal motion?
Air resistance and weight
Normal reaction and gravity
Weight and normal reaction
Applied push and kinetic friction
Which statement best summarizes a key characteristic of kinetic friction?
Acts only during motion and remains nearly constant
Acts at rest and decreases with force
Acts only at rest and varies widely
Acts during motion and increases with speed
When a block is pulled across a surface at constant velocity, what is true about its acceleration?
Acceleration is zero
Acceleration increases over time
Acceleration is constant positive
Acceleration is constant negative
At constant velocity while pulling a block, what is the net force on the block?
Net force equals weight
Net force equals normal
Net force equals pull
Net force is zero
Under constant velocity motion, how does the pulling force compare to the kinetic friction force?
They are equal in magnitude
Pulling force is greater
They act in the same direction
Friction force is greater
Increasing the block’s mass directly increases which force that leads to higher kinetic friction?
Normal force
Tension in string
Applied force
Gravitational field
Which statement best describes kinetic friction compared to static friction for a sliding block?
Kinetic friction increases speed
Kinetic friction acts during motion
Kinetic friction acts before motion
Kinetic friction equals zero always
Which variable in kinetic friction is dimensionless?
Pulling force magnitude
Coefficient of kinetic friction
Kinetic friction force
Normal force magnitude
Select the correct formula relating kinetic friction, coefficient of kinetic friction, and normal force.
Fk = N / μk
N = μk / Fk
μk = Fk · N
Fk = μk · N
If the normal force doubles while μk stays the same, what happens to the kinetic friction force?
It stays unchanged
It doubles in magnitude
It becomes zero
It becomes half as large
A 10 N pull moves a block at constant velocity. What is the kinetic friction force on the block?
10 N opposite motion
5 N opposite motion
0 N opposite motion
10 N same as motion
During constant velocity motion, which pair of forces must balance along the horizontal direction?
Pulling force and kinetic friction
Normal force and friction
Tension and weight
Weight and normal force
Which statement best describes the coefficient of friction?
An energy value stored in rough surfaces
A ratio with units that scales with mass
A force measured in newtons opposing motion
A unitless constant characterizing contact surfaces
Which factor directly affects the value of the coefficient of friction between two objects?
The temperature of surrounding air
The volume of the larger object
The materials in contact at the interface
The color of the sliding object
What do surface conditions like roughness and cleanliness influence most in sliding contact?
The electric charge distribution
The coefficient of friction value
The spring constant of the system
The object’s gravitational mass
How is the coefficient of friction commonly classified for motion states?
Conservative type and nonconservative type
Static type and kinetic type classifications
Elastic type and plastic type classifications
Translational type and rotational type
A block just begins to move when the applied force reaches a threshold. Which coefficient is relevant at that threshold?
Coefficient of static friction at the limit
Coefficient of kinetic friction during motion
Aerodynamic drag coefficient value
Average rolling resistance coefficient
Once a block is sliding steadily, which coefficient characterizes the frictional interaction?
Coefficient of kinetic friction while sliding
Coefficient of static friction at rest
Coefficient of drag in a fluid
Coefficient of rolling friction only
Which property do all coefficients of friction share regarding dimensions?
They are measured in joules per kilogram
They have dimensions of acceleration
They have units of newtons per meter
They are dimensionless with no units
Two clean, smooth metal surfaces versus two rough, dusty wooden surfaces. Which pair likely has the larger coefficient of friction?
Rough, dusty wooden surfaces pair
Clean, smooth metal surfaces pair
Both pairs have identical values
Neither pair exhibits any friction
Which change most likely reduces the coefficient of friction for a sliding interface?
Heating the room by several degrees
Painting the object a darker color
Increasing the object’s weight significantly
Cleaning and polishing the contacting surfaces
Which pairing correctly matches type with typical situation?
Kinetic: object held perfectly still
Static: just before motion begins
Kinetic: threshold when motion starts
Static: during steady sliding motion
Which relationship between kinetic friction force and normal force is shown in the graph?
Directly proportional linear relation
Inversely proportional curve
Quadratic increase with force
Constant friction independent of force
On a kinetic friction vs normal force graph, what does the slope of the line represent?
Surface area of contact
Applied pulling force
Mass of the block
Coefficient of kinetic friction
Which surface has the largest coefficient of kinetic friction based on the steeper line?
Smooth ice surface
Lubricated metal plate
Sandpaper surface
Highly polished table
Which observation correctly matches a shallower slope on the graph?
Less kinetic friction force
Greater kinetic friction force
Equal friction for all forces
Friction independent of normal force
If the normal force doubles for the same surface, what happens to kinetic friction according to the straight-line model?
It doubles proportionally
It halves proportionally
It increases unpredictably
It stays exactly constant
The equation relating kinetic friction and normal force for a surface is F_k = μ_k N. Which unit fits μ_k?
No unit, dimensionless
Newton per meter
Kilogram second squared
Pascal times meter
At a normal force of 6 N, which surface would show the largest kinetic friction on the plotted lines?
Sandpaper line
Rough table line
Polished table line
All lines show equal friction
Why do different surfaces produce different slopes on the same graph?
They alter gravitational acceleration
They have different μ_k values
They change the object’s mass
They have different normal force units
Which single change would decrease kinetic friction for the same normal force?
Increase surface roughness
Pull with a faster speed
Switch to a more polished surface
Increase object weight
A line on the graph passes through the origin. What does this imply about kinetic friction when normal force is zero?
Friction becomes infinite suddenly
Friction remains constant and nonzero
Friction oscillates around zero
Friction is zero at zero normal force
Which factor directly increases the magnitude of friction between two surfaces?
Lower mass of the moving object
Higher speed of motion at ordinary speeds
Larger surface area of a rigid object
Greater normal force pressing surfaces together
Which pair best describes variables that affect friction according to the slide?
Material types and normal force between surfaces
Surface area and temperature of the objects
Object volume and contact time
Speed of motion and direction of movement
For rigid objects, how does increasing surface area influence friction at ordinary speeds?
It reverses the direction of friction
It always decreases friction force
It linearly increases friction force
It has little to no effect on friction
Why does the type of materials in contact affect friction?
Different materials have different coefficients of friction
All materials exert identical resistive forces
Material type only changes surface area
Material type only changes object speed
Two blocks are pressed against a horizontal surface. Block A experiences a larger normal force than Block B. Which has greater friction if both materials are the same?
Neither experiences friction while stationary
Both have equal friction forces
Block B due to smaller contact area
Block A due to larger normal force
A skateboarder rolls faster across pavement. At ordinary speeds, how does speed affect the friction opposing motion?
Friction remains approximately the same
Friction skyrockets with speed
Friction reverses to push the skater
Friction becomes zero at higher speed
Which statement best explains a common misconception about friction and surface area for rigid bodies?
People think larger area means more friction, but it doesn’t
People think smaller area removes normal force entirely
People think area changes material type automatically
People think area is irrelevant for fluids, which is false
A wooden block is placed on steel and on ice with the same normal force. Where is friction larger and why?
On steel due to higher coefficient of friction
On ice because speed becomes very high
On ice due to lower normal force
Equal because surface area is unchanged
If the normal force between two surfaces doubles while material type is unchanged, what happens to the friction force (kinetic or static limit)?
It approximately doubles as well
It becomes half of the original
It changes unpredictably without relation
It becomes zero regardless of motion
A student claims that making a rigid sled wider will increase friction on snow at the same load. Evaluate the claim.
Incorrect because area reverses friction direction
Correct because area increases normal force
Correct because wider area increases contact
Incorrect because friction does not depend on area
Which statement best describes the normal force on an object resting on a surface?
Force due to gravity acting along the surface
Force exerted by surface perpendicular to itself
Force exerted by object along the surface
Force exerted by surface parallel to itself
Friction forces between two surfaces act in which direction relative to the surfaces?
Parallel to the surface
Perpendicular to the surface
At forty-five degrees to the surface
Randomly relative to the surface
If the normal force on a block doubles, what happens to the frictional force assuming the coefficient of friction is constant?
It doubles as well
It halves immediately
It becomes zero
It stays unchanged
Which pair of forces correctly matches their typical orientation for a block on a flat table?
Both normal and friction are perpendicular
Normal is parallel, friction is perpendicular
Normal is perpendicular, friction is parallel
Both normal and friction are parallel
A box is pushed across a floor. Which force resists its motion along the floor?
Friction force parallel to the surface
Applied force perpendicular to the surface
Normal force perpendicular to the surface
Gravitational force parallel to the surface
Which quantity directly influences the magnitude of kinetic friction for a given surface pair?
The object’s volume
The direction of gravity
The normal force magnitude
The horizontal area only
An object rests on a horizontal surface. Which statement is true about the normal force?
It acts in the direction of motion
It acts opposite to friction
It acts parallel to the surface
It acts perpendicular to the surface
A student claims friction can act perpendicular to the surface. Which correction should be made?
Friction acts parallel to the surface
Friction acts only downward
Friction acts opposite gravity
Friction acts only upward
On a rough horizontal surface, which change increases friction the most if the coefficient stays the same?
Removing the normal force
Decreasing the normal force
Tilting the surface slightly
Increasing the normal force
Which statement correctly compares friction and normal force for contact between two surfaces?
Friction is proportional to normal force
Friction is independent of normal force
Normal force is proportional to friction
Both are unrelated to contact strength
Which surface combination likely has the highest static friction coefficient μs?
Wood on wood has moderate resistance
Sandpaper on wood shows high resistance
Ice on ice exhibits very low resistance
Rubber on concrete shows very high resistance
Which pair most likely has both μs and μk very low?
Sandpaper rubbing against wood
Ice on ice with smooth contact
Rubber on concrete under dry conditions
Wood sliding on wood surfaces
For wood on wood, how does kinetic friction μk compare to static friction μs?
μk equals μs in all cases
μk is lower than μs overall
μk is unrelated to μs values
μk is higher than μs by a little
Which option best describes μk for rubber on concrete?
Moderate compared to its static value
Very low under typical conditions
Higher than the static coefficient
Exactly equal to the static value
Which combination indicates very high μs but only high μk?
Rubber on concrete during motion
Sandpaper on wood across surfaces
Wood on wood while sliding
Ice on ice at rest or motion
If an object starts moving only after a larger force, which coefficient is most relevant?
Net applied force during motion
Kinetic friction coefficient μk
Static friction coefficient μs
Normal force magnitude alone
A student claims rubber on concrete has lower μk than μs. Which evidence supports this?
Sandpaper increases grip when sliding
Objects stick more before moving
Tires skid easier once rolling
Ice slides with almost no pull
Which scenario would most likely require the least pushing force to keep motion going?
Rubbing sandpaper along wood
Sliding wood across wood steadily
Dragging rubber across concrete
Pushing ice across smooth ice
Why is μk for wood on wood labeled lower than μs?
Gravitational force decreases during motion
Kinetic friction grows with speed always
Static contact resists initial motion more
Surfaces bond more when sliding fast
A designer wants maximum grip at rest. Which pairing should be chosen?
Wood on wood for moderate grip
Sandpaper on wood for strong grip
Ice on ice for minimal resistance
Rubber on concrete for high grip
Which statement best describes surfaces at the atomic level when they appear smooth to the eye?
They are electrically neutral always
They are coated with invisible oil
They are rough with tiny asperities
They are perfectly flat everywhere
What initially makes contact when two solid surfaces touch each other?
Low valleys compress together
High points called asperities
Entire surfaces fuse uniformly
Large flat regions align
What occurs between atoms at the points of contact between two surfaces?
Atoms strongly repel
Atoms ionize and glow
Atoms temporarily bond
Atoms permanently merge
These microscopic bonds mainly do what during motion?
Increase mass of surfaces
Resist relative motion
Create sound vibrations
Enhance thermal conduction
Which types of friction are explained by microscopic bonding at contact points?
Static and kinetic
Rolling and fluid
Elastic and plastic
Thermal and magnetic
Why can smooth-looking surfaces still exhibit significant friction?
They are always slightly sticky
They trap air pockets inside
They are rough at atomic scale
They emit weak magnetic fields
A block at rest requires extra force to start sliding because of what microscopic effect?
Increased internal temperature
Uniform pressure distribution
Temporary atomic bonding
Balanced gravitational torque
Which misconception is corrected by the microscopic view of friction?
Friction only comes from surface roughness
Friction is caused by air resistance alone
Friction arises from bonding at asperities
Friction disappears on smooth materials
If contact area increases at atomic asperities, what is the most likely consequence for friction?
Friction decreases sharply
Friction remains unchanged
Friction tends to increase
Friction becomes negative
Why is the scientific understanding of friction still evolving?
Friction is not a physical phenomenon
Experiments cannot measure forces
The laws of motion were disproven
The exact bonding details are complex
