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 in the classroom on a string, or outdoors with 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 forwards/upwards. Third Law Newton's Laws of action-reaction.

The Third Law (action reaction) is also demonstrated with a rocket, either the film canister rocket or Baking soda and vinegar rocket demonstration.
A chemical reaction is used to build up gas pressure inside the rocket. As the gas exits downwards, it pushes on the rocket and makes it go upwards - action and reaction.
Newton's Second Law F=ma can be demonstrated in a rocket in two ways. We can either increase the force which increases the speed it goes up - this can be achieved by pushing the cork into the demonstration rocket harder (more gas pressure builds up before the cork exits). Or we can decrease the mass - turn the demonstration rocket upside down for launching and 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. (Note that it is best to use a dry cork, and dry the inside rim of the bottle, for this comparison as a wet cork slides out more easily. Try and push the cork in the same as before.)

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, but Newton's Laws are still happening.
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