Newton's 3rd Law

Newton's 3rd Law

Sir Isaac Newton, not Fig Newton

Sir Isaac Newton

Sir Isaac Newton

Sir Isaac Newton  (25 December 1642 – 20 March 1726/27 ) was an English mathematician, physicist, 

astronomer, theologian, and author (described in his own day as a "natural philosopher") who is widely recognized as one of the most influential scientists of all time and as a key figure in the scientific revolution.

​What is Newton's 3rd Law?

• ​Newton's 3rd Law of Motion states that, "Whenever one object exerts a force on a second object, the second object exerts equal and opposite force on the first object.

• Also known as: For every action there is an equal and opposite reaction.

• We call this the law of action/reaction.​

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​Force Pairs

• ​​The forces that two objects apply to each other.

• The objects are interacting. ​

• Action and Reaction Forces

• These two forces are equal in size and opposite in direction.

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​Newton's 3rd Law in space!

​Watch me please!

Grab some headphones from the front lab table if you need them!

​Example: Action/Reaction

​Example: Action/Reaction

Let's review...

• The Law of Action-Reaction.

• For every action there is an equal and opposite reaction.

• Forces come in pairs when acting on two interacting objects.

• The size of the force on one object is equal to the size of the force on a second object.

Multiple Choice

Newton’s law states that for every action, there is an ________ reaction.

• unequal and opposite

• equal and similar

• stronger and opposite

• equal and opposite

Multiple Choice

When a small car pushes a big truck, the truck applies an equal and opposite force on the car.

• False

• True

Multiple Choice

Newton's 3rd Law of motion states that....

• A object in motion/rest stays in motion/rest until it is acted upon by an unbalanced force.

• Force is equal to the mass and the acceleration of an object.

• For every action there is an equal and opposite reaction.

Multiple Choice

How do forces act on an object?

• They usually act alone

• They act in pairs

Multiple Choice

When a cannon fires a cannonball we observe Newton's third law. Which is the reaction force?

• The cannon moving forward

• The cannon moving backwards

• The cannonball moving backwards

• The cannonball moving forward

Multiple Choice

Action reaction forces never cancel each other out because

• They act on different objects.

• They act on the same objects

• They do not act on objects.

Multiple Choice

How is this an example of Newton's Third Law?

• Only the ball is applying a force to the soccer players head

• Only the soccer players head is applying the force to the ball

• The are both exerting an equal force on each other

Multiple Choice

How is this an example of Newton’s Third law?

• Only the ball is using the head

• They are both exerting an equal force on each other

• Only the head is pushing the ball

Multiple Choice

If two people with the same mass collide, they experience the same amount of force.

• True

• False

Multiple Choice

Action-reaction pairs can cause a change in motion.

• True

• False

Multiple Choice

A book rests on a table.  The force of gravity pulls down on the book with a force of 20 newtons. What prevents the books from accelerating downward ?   

• The table presses back up on the book with an equal and opposite force of 20 newtons.

• The table presses back up with a force greater than 20 Newtons

• The tale and the book together are accelerating downwards at 9.8 m/sec2

• The inertia of the book holds it up

Multiple Choice

When the person pushes the ground with their foot, the equal and opposite reaction force is

• the ground pushing back on their foot

• when they start to move forward

Multiple Choice

Force always come in________

• waves

• triplets

• pairs

Multiple Choice

What is another name for Newton's 3rd Law?

• The Law of Opposites Attract.

• Fig Newtons.

• The Law of Action-Reaction.

Multiple Choice

When a heavy football player and a light one run into each other, who exerts more force

• The light one

• Their force are equal

• The heavy one

Multiple Choice

For every action there is an equal and opposite reaction.

• True.

• False.

Multiple Choice

The forces in a force pair are in _______ direction

• opposite

• same

Multiple Choice

A person steps out of the boat and onto the dock.  As the person moves forward onto the dock, the boat moves backward.  Which statement best describes the backward motion of the boat as the person steps forward?

• For every action there is an equal and opposite reaction.

• Every mass exerts a force on every other mass.

• An object at rest tends to stay at rest.

• Friction opposes the motion of an object.

Multiple Choice

Why is the net force 0 in the image?

• Because the elephants are the same size

• Because they are both pulling the same amount of force in opposite directions

• Because they are elephants

• Because they are pulling away from each other.

Multiple Choice

If a 10 kilogram object accelerates suddenly at 15 m/s², how much force was applied to the object? (Hint: Use F=ma to solve.)

• 150 Newtons

• 15 Newtons

• 150 kilograms

• 100 kilograms

Example

A swimmer pushes back on the water and moves forward.

Multiple Choice

Which is the Action Force in this scenario: "A swimmer pushes back on the water and moves forward."

• A swimmer pushes back.

• A swimmer moves forward.

Multiple Choice

Which is the Reaction Force in this scenario: "A swimmer pushes back on the water and moves forward."

• A swimmer pushes back.

• A swimmer moves forward.

Multiple Choice

This picture shows .............

• Newton 2nd law of motion

• Newton 3rd law of motion

• Newton 1st law of motion

• I don't know

Multiple Choice

What will happen if the Action is greater than the Reaction?

• The man will fall

• The boat will sink

• Nothing will happen

Example

A rocket blasting off from the launch pad.

Multiple Choice

Which is the Action Force in this scenario: "A rocket blasting off from the launch pad."

• A rocket blasting off from the launch pad.

• The thrust of the fuel against the launch pad.

Multiple Choice

Which is the Reaction Force in this scenario: "A rocket blasting off from the launch pad."

• A rocket blasting off from the launch pad.

• The thrust of the fuel against the launch pad.

Multiple Choice

What happens to the balloon if the air is released ?

• Balloon goes right

• Balloon goes up

• Balloon goes down

• Balloon goes left

Multiple Choice

The two paired forces in Newton's third law:

• act on different objects

• are equal in size

• are opposite in direction

• are the same type

• all of the above

Example

A fireman turns on a hose and is knocked backwards.

Multiple Choice

Which is the Action Force in this scenario: "A fireman turns on a hose and is knocked backwards."

• The force of the water from the hose.

• The fireman is knocked backwards.

Multiple Choice

Which is the Reaction Force in this scenario: "A fireman turns on a hose and is knocked backwards."

• The force of the water from the hose.

• The fireman is knocked backwards.

1. Pick up a notecard from the front lab table.​

2. Front side - Neatly, write 3 important pieces of information about Newton's 3rd Law.

3. Back side - Draw, color, and label a diagram that demonstrates Newton's 3rd Law.

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​Brain Dump

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