Isaac Newton’s laws of motion explain the relationship between an object and the forces acting on it. The laws might seem very obvious today, but when Isaac Newton was alive they were revolutionary and formed the basis of modern physics. Isaac Newton built on ideas from Galileo Galilei, Jean Richer and Rene Descartes. It is also said that Edmund Halley convinced Isaac Newton to to write Principia.

Newton recorded his ideas about the laws of motion and gravity in a book now known as Principia.

Image of Isaac Newton, Principia, and F=ma
Isaac Newton’s Laws of Motion

A force is anything that can change the motion of an object. When you throw a ball you exert a force on it in a certain direction which is the direction in which it moves. The harder you throw, the further the ball travels as a bigger force is acting on it.

What are Newton’s Laws of Motion?

What is Newton’s First Law

An object at rest will remain at rest.

An object in motion will keep moving with the same speed and in the same direction unless another force acts on it.

Basically that means an object that is motionless, will stay motionless unless a force acts on it. Imagine a toy car on the floor, it will only move if someone gives it a push.

If the forces acting on a body are balanced it will move at a constant velocity.

Experiments to Demonstrate Newton’s First Law

A rocket mouse is a fantastic demonstration of Newton’s First Law. The cone on the milk bottle is at rest until the force of air being pushed out of the milk bottle ( when you squeeze it ) sends the cone flying into the air.

Milk Jug Rocket

Newton’s First Law is sometimes referred to as the Law of Inertia. This basically means that if an object is moving in a straight line it will continue moving in a straight line unless a force acts on it.

A good way to demonstrate this is with a simple inertia experiment.

inertia experiment using a glass, card, a cylinder and a lemon
Inertia experiment set up

If you pull the yellow card fast enough the black column will fall to the side and the lemon will fall in a straight line into the glass! The video below shows this in action.

What about friction?

We know that generally objects don’t continue moving forever, because they are slowed down by friction. A ball rolling on a carpet for example slows down much faster than a ball rolling on a smooth floor as there is more friction between a ball on a rough surface than on a smooth surface. You can demonstrate this by making a friction ramp.

In space where there is no friction from air, objects keep keep moving for much longer.

Newton’s Second Law

Newton’s Second Law is all about the relationship between the force applied to a body and the change in its momentum or acceleration.

Force is equal to mass times acceleration

f = ma

F – force applied ( N )

a – Acceleration (m/s2)

m – Mass ( kg )

What does that mean? Newton’s Second Law states that force is equal to mass times acceleration. A change in momentum is proportional to the change in the force applied.

Newton’s Second Law of Motion

Imagine kicking a light plastic football and a heavy football. It takes a lot more force to move the heavier ball the same distance as the lighter ball.

Newton’s Third Law

Every action has an equal and opposite reaction.

Newton’s Third Law states that for every action there is always an equal and opposite reaction. When one body acts on another, it experiences an equal and opposite reaction from the other body.

If you were to push an object, the objects pushes back against you and if you stopped pushing the force back against you stops as well.

Imagine a rocket launching. The downward thrust created by the engine is the action and the reaction is an opposite upward thrust forcing the rocket into the air.

A rocket will continue moving upwards as long as there is a resultant upwards force. If the upwards thrust force ceased the resultant force would be downwards.

Image showing a rocket taking off with thrust, weight, drag and resultant force marked,
Forces acting on a rocket at take off

Experiments to demonstrate all three of Newton’s Laws of Motion

A film canister rocket or mini bottle rocket is a great for demonstrating all three of Newton’s Laws.

Image of a film canister with a lego man attached by an elastic band.
Film Canister Rocket ready to launch!

Newton’s First Law

The film canister remains motionless unless something is added to create a force ( usually an effervescent vitamin tablet and water ).

Newton’s Second Law

Acceleration is affected by the mass of an object. If you increase the mass of the film canister you’ll find it moves more slowly and doesn’t fly as high.

Newton’s Third Law

The downward force on the film canister lid creates an opposite upwards force on the body of the canister which flies up into the air.

More experiments to demonstrate forces

Think about some of the difficulties astronauts experience in space with this hands on activity about docking with the ISS.

Find out more about Isaac Newton, Galileo and other famous scientists.

Learn about gravity with straw rockets, magnets and water bottles in this selection of easy gravity experiments.

Finally, try one of these easy investigations for learning about forces and motion.



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Originally posted at Science Sparks