Force and Motion Full Unit

Force and Motion

Learning Objectives

• Define motion and its reference frame.

• Describe forces and how they affect motion.

• Apply Newton's laws for motion, force, mass, acceleration.

• Calculate speed and use distance-time graphs.

• Motion is when an object's position changes from a reference frame.

• A reference frame is a place or object used for comparison.

• Fixed objects like trees or signs make good reference frames.

• Always state your reference frame to describe motion accurately.

What are Reference Frames and Motion?

Multiple Choice

What is a reference frame?

• The speed of an object

• A place or object used for comparison to determine if something is in motion

• The path an object follows

• A type of force

• Relative motion: object's movement depends on your viewpoint (reference frame).

• ​An object can be moving or still, depending on the reference frame.

• On a beach towel, you're still. But you zoom fast relative to the Sun!

• Roller coaster: still in your seat, but speeding past the ground!

What's the Deal with Relative Motion?

Multiple Choice

If you are sitting on a moving train, which of the following is true regarding your motion?

• You are only in motion relative to the train.

• You are in motion relative to the ground and stationary relative to the train.

• You are only stationary relative to the ground.

• You are not in motion according to any reference frame.

• Force is a push or a pull on another object.

• It's measured by strength (newtons, N) and has a direction.

• Forces change motion: speed up, slow down, or change direction!

• Arrows show force: length for strength, point for direction.

Force: The Push and Pull Effect!

Multiple Choice

How is the strength of a force represented by an arrow in a diagram?

• By the color of the arrow

• By the thickness of the arrow

• By the length of the arrow

• By the position of the arrow

​​Contact Forces: Touchy-Feely!

• Objects do not need to touch.

• Examples: gravity, magnetism, electrical forces.

• Gravity pulls objects with mass together.

​​Noncontact Forces: Action at a Distance!

Types of Forces: Contact vs. Noncontact

• Objects must touch for these forces.

• Examples: pushing a box, friction.

• Friction opposes motion between surfaces.

Multiple Choice

Which of the following is an example of a noncontact force?

• Pushing a shopping cart

• Friction between tires and the road

• The Earth's gravitational pull on the Moon

• Kicking a soccer ball

​​Balanced Forces

• Forces are unequal or not opposite.

• Object's motion changes. Vroom!

• Net force is not zero. It moves!

​​Unbalanced Forces

Forces: Balanced or Unbalanced?

• Equal forces push/pull opposite ways.

• Object's motion stays the same.

• Net force is zero. No change!

Multiple Choice

What happens to an object when unbalanced forces act upon it?

• The object remains at rest.

• The object's motion does not change.

• The object's motion changes (it accelerates).

• The net force on the object becomes zero.

• Speed: How fast an object moves, or distance covered per unit time.

• Formula: Speed = Distance / Time.

• Units: Measured in m/s (SI), km/h, or mph.

• Example: Skier covers 50m in 10s. Speed = 50m / 10s = 5 m/s.

Calculating Speed

Multiple Choice

A car travels a distance of 200 kilometers in 4 hours. What is its speed?

• 50 km/h

• 800 km/h

• 0.02 km/h

• 204 km/h

​​Instantaneous Speed

• Total distance divided by total travel time.

• Formula: Total Distance / Total Time.

• Gives an overall speed for the journey.

​​Average Speed

Concept 7: Instantaneous and Average Speed

• Speed of an object at one specific instant.

• A car's speedometer shows this speed.

• It can change often during travel.

Multiple Choice

A cyclist travels 10 km in the first hour and 15 km in the second hour. What is their average speed over the two hours?

• 10 km/h

• 12.5 km/h

• 15 km/h

• 25 km/h

• A distance-time graph shows time (x-axis) and distance (y-axis).

• The line's slope tells you the speed. Slope = Rise / Run.

• Steeper slope means greater speed. A flat line means zero speed.

• Example: Rise 50m, Run 2s. Speed = 50m / 2s = 25 m/s.

Calculating Speed from Distance-Time Graphs

Multiple Choice

On a distance-versus-time graph, what does the slope of the line represent?

• Acceleration

• Distance traveled

• Time taken

• Speed

• Velocity is speed in a particular direction.

• It always includes both speed and direction.

• Change speed or direction, velocity changes too!

• Direction is vital for things like storms or planes.

Concept 9: Velocity

Multiple Choice

What information is needed to describe an object's velocity?

• Speed only

• Direction only

• Speed and direction

• Distance and time

• Acceleration is how quickly velocity changes.

• It happens when an object speeds up.

• Slowing down is also acceleration (deceleration).

• Changing direction, even at constant speed, is acceleration.

Acceleration

Multiple Choice

Which of the following situations describes an object that is accelerating?

• A car moving at a constant speed of 50 km/h in a straight line.

• A runner jogging at a constant speed around a circular track.

• A book resting on a table.

• All of the above.

• Moving objects have 'energy of motion' (kinetic energy).

• When objects collide, they can push each other with a force.

• This force can make a still object start to move.

• Collisions also transfer this energy of motion between objects.

Crash Course: Forces & Energy in Collisions!

Multiple Choice

When a moving bumper car hits a stationary bumper car, causing it to move, what is one way to describe what happens?

• The stationary car creates energy.

• The moving car transfers some of its energy of motion to the stationary car.

• No forces are involved in the collision.

• The moving car gains energy from the stationary car.

• An object at rest will stay at rest.

• ​An object in motion stays moving at constant velocity.

• This happens unless a net (unbalanced) force acts on it.

• This resistance to motion change is called inertia.

Newton's First Law of Motion (Law of Inertia)

Multiple Choice

According to Newton's first law of motion, what will happen to an object moving at a constant velocity if no net force acts on it?

• It will gradually slow down and stop.

• It will speed up.

• It will continue moving at that constant velocity.

• It will change direction.

• Inertia is an object's resistance to changes in its state of motion.

• Newton's first law is also known as the law of inertia.

• More mass means more inertia, making it harder to change an object's motion.

• When a car stops, your body lurches forward due to inertia.

Inertia and Mass

Multiple Choice

How does an object's mass relate to its inertia?

• Mass and inertia are unrelated.

• The less mass an object has, the greater its inertia.

• The more mass an object has, the greater its inertia.

• Mass is a type of force, while inertia is a type of motion.

• Acceleration changes with net force and an object's mass.

• The main formula is F = ma (Force = Mass × Acceleration).

• More force = more acceleration. More mass = less acceleration (like the sleighs!).

• Also a=F/m, m=F/a. Units: N (Force), kg (Mass), m/s² (Accel). 1N = 1kg·m/s².

Newton's Second Law of Motion

Multiple Choice

According to Newton's second law (F=ma), if the net force acting on an object doubles, and its mass remains constant, what happens to its acceleration?

• It is halved.

• It remains the same.

• It doubles.

• It quadruples.

• Every action has an equal and opposite reaction force.

• Forces always occur in pairs, called action-reaction pairs.

• These forces act on different objects, so they don't cancel.

• Walking: Foot pushes ground (action), ground pushes foot (reaction).

Newton's Third Law of Motion

Multiple Choice

A student pushes against a wall. The wall pushes back on the student with an equal and opposite force. Why don't these forces cancel each other out?

• The forces are not equal in strength.

• The forces act in the same direction.

• The forces act on different objects (the student and the wall).

• One of the forces is not a real force.

• Friction is a contact force when surfaces rub together.

• It acts opposite to the object's motion or attempted motion.

• Surface type matters: smooth surfaces have less friction.

• Pressing surfaces harder together increases the friction.

Friction and Its Factors

Multiple Choice

What are the two main factors that affect the amount of friction between two surfaces?

• The speed of the object and its mass

• The types of surfaces involved and how hard they are pushed together

• The color of the surfaces and the air temperature

• The direction of motion and the object's shape

• Static Friction: The 'stay-put' force for objects at rest!

• Sliding Friction: The 'slow-down' hero when surfaces rub together.

• Rolling Friction: Wheels' best friend, making rolling easy!

• Fluid Friction: The 'drag' you feel moving through water or air.

Types of Friction

Multiple Choice

What type of friction occurs when a solid object moves through a fluid like air or water?

• Static friction

• Sliding friction

• Rolling friction

• Fluid friction

​​Gravity on Earth

• Gravity acts between all objects with mass.

• Any two objects with mass attract.

• Sun's gravity holds planets in orbit.

​​Law of Universal Gravitation

Concept 18: Gravity and the Law of Universal Gravitation

• A force pulling objects to Earth.

• Pulls them towards Earth's center.

• Makes objects fall down.

Multiple Choice

What does the law of universal gravitation state?

• Only planets have gravity.

• Gravity only acts on objects on Earth.

• The force of gravity acts between all objects in the universe that have mass.

• Gravity is a contact force.

• Mass is key: Greater mass means stronger gravitational force.

• ​Example: The Sun's large mass creates very strong gravity.

• Distance also matters: Greater distance means weaker gravitational force.

• Gravity weakens a lot with distance (inverse square relationship).

Factors Affecting Gravitational Force

Multiple Choice

If the distance between two objects increases, what happens to the gravitational force between them?

• It increases.

• It decreases.

• It remains the same.

• It becomes zero immediately.

​​All About Mass

• Measures gravity's pull on an object.

• Its SI unit is the newton (N).

• Changes with gravity (W = m × g).

​​What is Weight?

Concept 20: Weight and Mass

• Measures the amount of 'stuff' in an object.

• Its SI unit is the kilogram (kg).

• Your mass stays the same everywhere!

Multiple Choice

What is the difference between mass and weight?

• Mass is a force, weight is the amount of matter.

• Mass is measured in Newtons, weight in kilograms.

• Mass is the amount of matter and is constant; weight is the force of gravity and can change with location.

• There is no difference; they are the same.

• Kinetic energy is the energy an object has due to its motion.

• It depends on two things: the object's mass and its speed.

• More mass means more kinetic energy if speed stays the same.

• More speed means MUCH more kinetic energy (KE = 1/2 mv²)!

Kinetic Energy: Energy on the Move!

Multiple Choice

What are the two factors that determine an object's kinetic energy?

• Its weight and height

• Its mass and speed

• Its volume and temperature

• Its direction and acceleration

​Correction

• Constant motion needs no net force. Force *changes* motion.

• Objects fall at the same rate without air resistance.

• Inertia isn't a force. It resists motion changes.

• Action-reaction forces act on different objects, so they don't cancel.
  

​Misconception

Common Misconceptions

• Motion requires a force in its direction.

• Heavier objects always fall faster.

• Inertia is a force that keeps objects moving.

• Action-reaction forces cancel, preventing motion.
  

Summary

• Motion happens when things change position from a reference point. Groovy!

• Forces are pushes or pulls that make things speed up, slow down, or turn.

• Newton's awesome Laws show how forces and motion work together.

• Kinetic energy is motion energy! Gravity and friction are super important forces.

Open Ended

What are the two main factors that affect the strength of gravitational force between two objects?

Poll

If a car is traveling at a constant speed of 60 mph but turns a corner, is it accelerating? Explain why or why not.

• Yes, because its speed changed

• Yes, because its direction changed

• No, because its speed is constant

• No, because it didn't slow down

Open Ended

Briefly state Newton's First Law of Motion in your own words.

Poll

On a scale of 1-4, how confident do you feel about applying Newton's Laws to solve problems? (1=Not confident, 4=Very confident)

• 1

• 2

• 3

• 4

Open Ended

What concept from today's lesson on Force and Motion was most challenging for you to understand?