A push or pull on an object.
Force
A passenger moves forward when a car suddenly stops.
Newton's 1st Law
(Objects in motion stay in motion)
A wagon has a mass of 5 kg and accelerates at 2 m/s². How much force is applied? Label your answer with N for Newtons.
Force = mass x acceleration
10 N
Why does a skateboard eventually slow down even if nobody stops it?
Friction slows objects down by working in the opposite direction of the moving object.
A swimmer pushes water backward. What is the reaction force?
The water pushes the swimmer forward.
The tendency of an object to resist changes in motion.
Inertia
An empty shopping cart speeds up more than a full shopping cart when pushed with the same force.
Newton's 2nd Law
(Force is mass x acceleration)
A wagon has a mass of 8 kg and accelerates at 3 m/s². How much force is applied? Label your answer with N for Newtons.
Force = mass x acceleration
24 N
A passenger lurches forward when a car suddenly stops. Explain using Newton's 1st Law.
The passenger's body wants to keep moving forward because objects resist changes in motion.

A basketball player jumps off the floor. What force pushes the player upward?
The floor pushes up on the player.

The rate at which an object's velocity changes.
Acceleration
A rocket pushes gas downward and moves upward.
Newton's 3rd Law
(For every action, there is an equal and opposite reaction)
Two objects are pushed with the same force. One has a mass of 2 kg and one has a mass of 10 kg. Which accelerates faster?

The 2 kg object
A student pushes a 2 kg box and a 10 kg box with the same force. Which accelerates more and why?

The 2 kg box accelerates more because less mass means greater acceleration for the same force.
A rocket pushes exhaust gases downward on the ground. What is the reaction force?
The ground pushes the rocket upward.

A force that acts through direct touching.
Contact force
A soccer ball sits still until someone kicks it.
Newton's 1st Law
(An object at rest stays at rest)
An object has 25 N pushing right and 10 N pushing left. Which direction will it move?

Right
Two students pull on a rope with equal force in opposite directions. What happens and why?

The rope stays in place because the forces are balanced.
A person jumps from a boat onto a dock. The boat moves backward.
-What is the action force?
-What is the reaction force?
Action: The person pushes backward on the boat.
Reaction: The boat pushed the person forward.
A force that acts without direct touching.
Non-contact force
A swimmer pushes water backward, and their body moves forward.
Newton's 3rd Law
(For every action, there is an equal and opposite reaction)
An object has 30 N pushing right and 30 N pushing left. What happens?

It stays in place (balanced forces)
An object has 20 N pushing right and 12 N pushing left. Explain where the object moves.

The object moves right.
You design a barrier to protect plastic cups from a toy car. Explain how Newton's 3rd Law helps protect the cups.
When the car hits the barrier, the barrier pushes back on the car with an equal force. This stops or slows the car before it reaches the cups.
