Have you heard of Newton’s first law? It’s also called the law of inertia. This law states that if an object is at rest, it will remain at rest unless acted upon by an external force. Similarly, if an object is in motion, it will continue moving in a straight line at a constant speed unless something changes its motion or direction.
What does this look like in practice?
An object at rest will stay at rest…
..unless acted upon by an external force.
A moving object will keep moving at a constant speed and direction…
…unless acted upon by an external force.
Examples
Tools on a Table
Imagine placing a fork on a table. It will stay exactly where you left it until something moves it. This shows that objects at rest stay at rest unless affected by a force.
Riding a Bus
When a bus suddenly starts moving, you might feel yourself sway backward. When the bus suddenly stops, you might feel your body lean forward. These movements happen because of inertia—your body wants to maintain its initial state, whether at rest or in motion.
Riding a Bicycle
When riding a bicycle, if you stop pedaling, the bike will continue moving forward for a while. This happens due to inertia, but eventually, the bike will stop because of friction with the ground and air resistance.
Newton’s first law shows how objects tend to maintain their current state—if they are at rest, they’ll stay at rest, and if they are in motion, they’ll keep moving in a straight line at a constant speed until something stops them or changes their direction.