Newton's First Law
Newton's first law states that an object stays at rest or moves at constant velocity unless a resultant force acts on it.
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Newton's first law states that an object stays at rest or moves at constant velocity unless a resultant force acts on it.
- This property is called inertia
- Balanced forces mean no change in motion
- Seat belts protect passengers using this law
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Newton's First Law?
Within Physics, which covers forces, energy, waves, electricity, magnetism, light and space explained through motion and experiments, this topic explains Newton's First Law. Physics topics explain how things move, push, heat up and carry energy, so each one here pairs a definition with a live model you can change.
Check that you can explain Newton's First Law in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Newton's First Law explains how the physical world behaves, from sport and transport to electricity and medicine.
Newton's First Law in detail
Newton's first law states that an object stays at rest, or keeps moving at constant velocity in a straight line, unless acted on by a resultant force. This property of resisting changes in motion is called inertia, and greater mass means greater inertia.
It explains why passengers lurch forward when a car brakes suddenly and why a spacecraft far from any force keeps coasting. Balanced forces (zero resultant) mean no change in motion, which does not necessarily mean the object is stationary. The law overturned the old belief that a force is needed to keep things moving.
How the interactive helps you understand Newton's First Law
Watch the force arrows in the interactive. Use any sliders or buttons it offers to change the values and see how the force arrows responds.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Newton's First Law.
Real-life uses and examples
- Explain everyday devices, such as brakes, lifts or chargers, using Newton's First Law.
- Use Newton's First Law to make sense of a practical and its results.
- Answer “explain” questions by linking Newton's First Law to a clear cause and effect.
Common mistakes to avoid
- Forgetting that some quantities, such as force or velocity, also have a direction.
- Mixing up Newton's First Law with a related quantity that has different units.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Newton's First Law
What is Newton's First Law?
Newton's first law states that an object stays at rest or moves at constant velocity unless a resultant force acts on it.
What are the most important points about Newton's First Law?
The main points are: This property is called inertia; Balanced forces mean no change in motion; Seat belts protect passengers using this law.
Why is Newton's First Law useful?
Understanding Newton's First Law explains how the physical world behaves, from sport and transport to electricity and medicine.
How can I practise Newton's First Law?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Newton's First Law?
Related topics in Physics include Mass and Weight, Resultant Forces, Hooke's Law and Springs.