Sir Isaac Newton (1643 - 1727) was an English mathematician, physicist, astronomer, alchemist, theologian and author. He wrote the Laws of Motion in 1687. They were the dominant scientific viewpoints for centuries until Albert Einstein's theory of relativity in the early 1900s.
There are three Laws of Motion. They explain everything from why cars stop when brakes are applied to how rockets propel themselves into space. The laws are fundamental to GCSE combined science, where your understanding is tested with questions on everyday situations and natural phenomena.
This article will explore each of Newton's Laws of Motion. We will break each law down clearly and provide examples of its application. This revision guide is suitable for all exam boards, including AQA, OCR and Edexcel. If you need help revising for your GCSE Physics AQA revision, TeachTutti has GCSE Physics tutors who can teach you online or in person. Our tutors will tailor lessons to your needs, such as preparing GCSE Physics revision notes.
First Law - Inertia
Newton’s First Law of Motion is also known as the law of inertia. It can be used to explain the movement of objects travelling with uniform motion (constant velocity). Put another way, it describes how an object behaves when there are no external forces:
"An object will remain at rest, or move at a constant speed in a straight line, unless acted upon by a resultant external force."
This statement may sound counterintuitive. For example, if you roll a ball across a field, eventually it will stop. In fact, this action confirms the law: the ball stops because of external forces, such as friction from the grass or resistance in the air. The ball would continue to roll if no forces were imposed on it.
Here are further examples of Newton's 1st law of inertia:
- Passengers in a vehicle - Passengers will jerk forward when a bus suddenly brakes. This displays inertia as bodies will continue moving until stopped by an external force, e.g. seatbelts.
- Sliding objects - Trying to pull a tablecloth from underneath plates relies on inertia. If you do the trick correctly, the plates will initially remain still as there's minimal force acting on them.
Inertia explains the need for seatbelts, why spacecraft can travel effortlessly through space after liftoff and why objects behave the way they do when forces act on them.
1
What force will cause a hockey puck sliding across smooth ice to eventually stop?
Second Law - Force, mass & acceleration of an object
Newton’s Second Law builds on our understanding of how forces affect motion. The formula for this law is as follows:
Force (F) = mass (m) × acceleration (a)
The law means that an object has greater acceleration if a larger force is applied. It also states that an object will have a smaller acceleration for this amount of force if the object has a greater mass.
For example, let's say we have an empty and a full shopping trolley. The acceleration on the empty trolley is far greater because it has less mass. If you wanted to push the loaded trolley with the same speed, the resultant force must be far greater.
This law explains why lorries and trucks need more powerful engines, compared to a sports car that accelerates far more quickly with a smaller engine.
Here is a practical example of this law:
- Football - When you kick a football hard, you apply greater force. This makes the ball accelerate faster and move further. The mass of the football hasn't changed, but the increased force results in greater acceleration.
2
What happens if you double the force on an object and the mass doesn't change?
Third Law - Action and Reaction
The third law of motion states:
"For every action, there is an equal and opposite reaction."
Put another way, when two objects interact, they exert the same force in opposite directions. We see this concept all around us. For example, the action of stepping off a small boat onto land causes the boat to move backwards (the reaction). These actions happen at exactly the same time.
Another example is a rocket launching into space. The gases that are expelled downwards (action) and the resultant vertical acceleration (reaction) are directly linked, launching the rocket into the air. Both of these examples clearly show the equal and opposite forces.
Here are further everyday examples:
- Jumping - You push down on the ground, and the ground pushes you upwards.
- Swimming - Your arms push water backwards, and the water pushes your body forwards.
- Balloon - When air escapes from a balloon, the balloon moves forward with the same driving force.
3
Why does a skateboard roll backwards when you jump off it?
Practical applications and experiments
There are experiments and real-world applications of Newton's Laws that reinforce their meaning. The practical examples below show how theoretical ideas work in the real world:
- Coins and cards (Newton’s First Law) - Put a card on top of a glass and place a coin on this card. When you flip the card, the coin will drop into the glass. The coin stays in place (inertia) until gravity pulls it down when the card is removed.
- Trolley and weights (Newton’s Second Law) - Attach weights of differing amounts to a trolley using a string over a pulley. The trolley will accelerate faster as the weight/force increases. This shows that F = m x a.
- Balloon rocket (Newton’s Third Law) - Inflate a balloon without tying it. When you let it go, the air will rush out and push the balloon in the opposite direction. This shows action and reaction forces.
These principles are the foundation for engineering, sports science and space travel. You could also try designing your own experiment based on the ideas above to demonstrate one of Newton's Laws and reinforce your understanding.
4
What experiment shows Newton’s Third Law?
Final thoughts on Newton's Laws - GCSE Physics
Newton’s laws on the motion of objects are the backbone of classical physics. They explain how and why objects move, from everyday events, like riding a bike, to advanced technologies, such as jet engines.
We now understand the following:
- Newton’s First Law - Motion only changes when a force is exerted on the object. It won't speed up, slow down or change direction without force, such as a frictional force.
- Newton’s Second Law - The link between force, mass and acceleration is shown in the formula F = m x a.
- Newton’s Third Law - Forces always come in pairs. Every action produces an equal and opposite reaction.
For further learning, you can read Britannica's biography on Isaac Newton. You can also test your knowledge with past paper questions on Newton's Laws by Physics and Maths Tutor.
If you need help learning about Newton's Laws or related topics, TeachTutti has qualified GCSE Physics tutors. Lessons can be online or in-person, and tutors will tailor lessons to your specific needs, such as preparing First Law GCSE revision notes.
