Mass, Weight, Friction

Things to think about before we get started...

Noncontact Forces

• A contact force is a push or a pull on one object by an object that is touching it

• Contact forces can be strong or weak

  • weak: pressing buttons on a game controller

  • strong: tectonic plates shifting and causing earthquakes

Contact Forces

Types of Forces

• A noncontact force is a force that one object can apply to another object without touching it

• Gravity is a noncontact force

• Magnetic forces and electric forces are also noncontact forces

Multiple Choice

If you push a book down and push another book across your desk with the same amount of force, is the outcome the same?

• Yes

• No

Multiple Choice

A force that one object can apply to another object without touching is?

• Gravity

• Noncontact Force

• Friction

• Contact Force

​Contact forces are applied when one object touches another.

​​Contact force

Friction: a contact force that two surfaces exert on each other when they rub against the other. ​

• Rubbing your hands together quickly.

• Walking and not slipping​

​​Example

​

​Noncontact forces are applied to an object whether it touches the object or not.

​​Noncontact force

​

​Gravity: A force that pulls objects toward each other as a result of their masses.

• ​You and the Earth

• ​Magnets

• Electricity​

​​Example

Multiple Choice

leaves blowing in the wind is an example of a

• contact force

• noncontact force

Multiple Choice

magnet attracting a nail

• contact

• noncontact

Multiple Choice

a leaf falling from a tree

• contact

• noncontact

Multiple Choice

a bat hitting a baseball

• contact

• noncontact

Multiple Choice

pushing in a chair

• contact

• noncontact

Multiple Choice

A wheeled cart is moving to the right at a constant speed.  Two forces of equal magnitude are acting upon the cart. Which of the following best describes the forces and motion of the cart?

• Balanced Forces, Constant Speed
• Balanced Forces, Acceleration
• Unbalanced Forces, Constant Speed
• Unbalanced Forces, Acceleration

Multiple Choice

Which of the following is an example of an unbalanced force?

Multiple Choice

The three examples pictured are of

• Non-contact Forces

• Contact Forces

Multiple Choice

Normal force is a...

• Contact Force

• Non-Contact Force

Multiple Choice

A contact force is from

• objects physically touching

• far apart objects

• not touching object

• always a pull

Multiple Choice

What is a NON-CONTACT force?

• A push or pull force where the objects are not touching

• A push force where the objects are touching.

• An example would be pulling open a door.

• The only type of force that exists in the world.

Multiple Choice

What are the three NON-CONTACT forces we are studying this unit?

• Gravity, friction, air resistance

• Forces, motion, human body systems

• Friction, electricity, muscular system

• Gravity, electricity, and magnetism

Multiple Choice

What is the net force being applied to the couch?

• 5N RIght

• 5 N Up

• 45 N Right

• 25 N Right

Multiple Choice

What is the FORCE? 

• 5 N
• 10 N
• 400 N
• 0 N

Multiple Choice

What is the net force?

• 17 N Right
• 3 N Right
• 3 N Left
• 17 N Left

Multiple Choice

Which direction will the object move?

• Up
• Down
• Right
• Left

Multiple Choice

Calculate the net force shown in the  diagram?

• 41 N
• 25 N
• 16 N
• 9 N

Multiple Choice

What is the net force?

• 65 N left
• 65 N right
• 35 N left
• 35 N right

Gravity

Multiple Choice

Can you see gravity?

• Yes

• No

Scientists have observed the motion of falling objects and the
motions of planets for many years.

Although scientists could not see gravity, they could see its
effects.

Gravity is a force of attraction between objects due to their
mass.

Gravity is always an attractive force because it always pulls
objects towards each other.

Force is a push or a pull upon an object resulting from the
object’s interaction with another object.

Multiple Choice

Force is a push or a pull upon an object resulting from the object’s interaction with another object.

• True

• False

What is weight?

Mass: is the amount of matter in an object

Weight: is a measure of the pull of the gravity on that mass. Weight is a force.

Our weight on Earth is how much force the Earth gravity has on us and how hard it
is pulling us towards the surface

Think of it this way.

An object is made up of a certain amount of matter, so its mass is constant.

The object has a certain weight due to the force of gravity.

If the force of gravity decreases, the weight of the object decreases. If the force of
gravity increases, the weight of an object increases.

Mass and Weight

A common unit for mass in the metric system is in grams (g) or kilogram (kg).

Scientist measure forces with newton (N), a unit named after Isaac Newton.

Ex. An apple with a mass of about 102g weighs 1N on Earth.

Universal Law of Gravitational

• Any two objects in the universe are attracted to each other by a force called gravity

• Gravitational force is affect by two factors: (1) mass & (2) distance

• Mass is measured in kilograms and grams

• Distance is measured in kilometers

• Weight is measured in Newtons.

Effect of Mass & Distance on Objects on Gravity

• Mass of an object increases ↑, gravitational force of an object increases ↑

• If distance between objects decreases ↓, gravitational force between objects increase ↑

• 
  

• 
  

• 
  

Multiple Choice

Increasing which factor will cause the gravitational force between two objects to decrease?

• weights of the object

• distance between the objects

• acceleration of the objects

• masses of the objects

Forces that Can Affect Something Falling

• Two forces that affect something falling: gravity & air resistance

• 
  

Terminal Velocity

• Force of gravity and force of air resistance are equal to zero

• Acceleration is also zero.

Free Fall

• When the only force acting on a falling body is gravity, it is called free fall.

• Air Resistance → Objects with less surface area will fall faster

• No Air Resistance → in a vacuum (objects will fall at the same rate & gravity only)

Projectile Motion

• Gravity can cause a thrown object to move in a curved, downward path called projectile motion

• Inertia causes ball to move horizontally, gravity causes the ball to move vertically

• 
  

Universal Gravity

• Newton realized that gravity acts all around us, not just on the Earth

  • Including Space

• The Law of Universal Gravitation: The force of Gravity acts between all objects that have mass

  • Anything that has mass feels a pull towards the objects with mass around them

  • Keeps the Planets in Orbit

If objects with Mass are attracted to one another, why do they not fly off into space toward each other? 

Factors Affecting Gravity

• The Gravitational force between some objects is stronger than the force between others

• There are two factors that affect how Gravity acts on objects: Mass and Distance

  • Mass: The larger an object is, the larger its pull on other objects

  • Distance: The farther apart two objects are, the weaker they pull on each other

Ocean Tides & Gravity

• ​The tides are connected to the moon through the force of Gravity

• As the moon revolves around the Earth, the force of Gravity changes depending on which side of the Earth it is on​

Weight vs. Mass

• Mass and Weight are not the same things

  • Mass Measures how much matter is in an object.

  • Weight measures how much force gravity exerts on an object

    • weight can vary based on where you are in the universe, depending on the gravitational pull in a certain place

Multiple Choice

The force of gravity on a person or object on the surface of a planet is called

• mass.

• weight

• Terminal Velocity

• free fall.

Friction

Multiple Choice

The rougher the surface, the faster an object will travel over the surface.

• True

• False

Multiple Choice

Which of the following is an example of friction that is harmful?

• Pencil marking on paper
• Engine parts wearing out
• sand placed on ice in the winter
• Using an eraser to erase marks

Multiple Select

Why are the soles of shoes and tyres of vehicles grooved?

• To increase friction

• To reduce friction

Open Ended

Why do gymnasts apply a coarse substance to their hands?

Multiple Choice

Which would NOT be a way of reducing friction?

• making the surfaces smoother
• using lubricants such as waxes, oils, or grease
• changing from sliding friction to rolling friction using ball bearings
• Using kitty litter on snow and ice to help your car gain traction

Multiple Choice

Why is it important for basketball players to wear shoes with tread when playing?

• to increase the speed of the player

• to decrease the force between the player and the floor

• to decrease the amount of force needed for the player to move

• to increase friction between the floor and the player’s feet

Multiple Choice

Which parachute was moving faster?

Multiple Choice

Which parachute is moving slower because there is more air resistance?

Multiple Choice

True or False:

A skydiver jumps from an airplane with a parachute. Gravity pulls her down and friction slows her fall.

• False

• True

Multiple Choice

A man is pushing a ball up a hill. If the man stops pushing the ball and steps out of the way, what will most likely happen to the ball?

• It will stop on the hill.

• It will roll down the hill.

• It will roll to the side toward the man.

• It will fly.

Multiple Choice

What are the four types of friction?

• Pulling, Pushing, Rolling, and Sliding

• Fluid, Sliding, Rolling and Static

• Fluid, Pushing, Pulling, and Rolling

• Pulling, Pushing, Static, and Sliding

Word Cloud

What is a force?

Understand how to calculate net force:

Multiple Choice

If there are two forces going in opposite directions how would you find the net force?

• Subtract

• Add

• Divide

• Multiply

Multiple Choice

Forces that have a net force of zero ( the object is still).

• Balanced force
• Unbalanced force

Multiple Choice

If a person is picking up a book with the force of 50 N and the gravity is pulling down with 15 N, what is the net force?

• 50 N dup

• 35 N up

• 65 N up

• 35 N down

​Graphing Motion:
Distance-Time Graphs
Velocity-Time Graphs

Multiple Choice

What does this graph represent?

• Constant Speed
• Acceleration
• Not moving

Multiple Choice

What does this graph represent?

• Constant speed
• Acceleration
• Not moving

Multiple Choice

Match the description to the graph:

"The car is coming back."

Multiple Choice

In which of the following graphs below are both runners moving at the same speed?

Multiple Choice

Which section represents a steady speed?

• A

• B

• C

• D

Multiple Choice

Use the graph above and pick the most accurate description of the object's motion

• object is moving at constant speed

• object is speeding up

• object is at rest

• object is slowing down

Poll

How do you feel about forces so far?