Lesson plan

Newton's Laws

Force activities with a focus on Newton's Third Law.
Science content
Physics: Motion and Forces, Newton’s Laws, Gravity (K, 2, 6)

This lesson is best done once students have been introduced to Newton's Laws:
First Law - objects will stay stopped or in constant motion until a force acts on them (which might make them stop or start or change direction)
Second Law - F=ma: for a constant force a smaller mass will accelerate more than a larger mass; a greater force will make the same mass accelerate more.
Third Law - for every action there is an equal and opposite reaction; when an object pushes on another it gets pushed back with equal force.

Balloon rocket activity as a demonstration in the classroom, or outdoors. No string-let it fly free.
Discuss why it flies - the air is under pressure in the balloon so it rushes out of the hole. As it leaves it pushes back on the balloon exerting a force on the balloon which sends it upwards. This is Newton's Laws in action, demonstration the action-reaction of the Third Law.

Model how real rockets work with the film canister rocket or Baking soda and vinegar rocket demonstration.
To build up gas pressure in the gas chamber a chemical reaction is used.
The exiting gas pushes back on the rocket to make it go upwards - Newton's Third Law at its best.
To make it go higher, we need more gas leaving the chamber which will exert a greater force (Newton's Second Law) - this can be achieved by pushing the cork into the demonstration rocket harder (more gas pressure builds up before the cork exits.
F=ma (Third Law) is nicely and dramatically demonstrated by turning the demonstration rocket upside down for launching - with the same amount of baking soda and vinegar (same force) the smaller mass of the cork means that it is shot way higher than the greater mass of the whole rocket.

Use molecule models to show how the baking soda and vinegar make gas.
Show the chemical reaction for real rockets.

Airplanes have more complex forces than rockets.
Students make paper airplanes, followed by discussion of the balance of forces that keep them in the air.
Lift is from Newton's Third Law - as the airflows off the wing it flows downwards. This downwards flow of air pushes back up on the wing, making a lifting force.
Allow students to experiment with tailoring their airplanes with the forces in mind.

The catapult demonstrates all three Laws - change the ammo weight to see how the same force makes it go further, or the elastic band tension to see how a greater force gives greater acceleration.

Balancing sculpture demonstrates forces in balance - the sculpture settles where the forces balance each other out.

Grades taught
Gr 5
Gr 6
Gr 7