### Newton's First Law

N(I) in words
If an object is at rest, it will remains at rest, and if an object is already moving at a constant velocity, it will continue to move at that constant velocity, unless acted upon by a resultant force.

Newton (I) is about the absence of a resultant force!

Newton's First Law refers to an objects Inertia.
Inertia is that property of matter that keeps resting objects at rest, and keeps moving objects moving!

Inertia
• An object remains resting due to its INERTIA.
• An object remains moving (at constant velocity) due to its INERTIA.
• An objects MASS indicates its INERTIA.
Larger masses have larger INERTIAS, making them more difficult to move or to stop.

Force
• Only a resultant force can make a resting object move, or change the velocity of a moving object.
• If an object is at REST, the RESULTANT FORCE = ZERO
• If an object is moving at CONSTANT VELOCITY the RESULTANT FORCE = ZERO
• In other words, if the forces acting on an object are balanced (FR = 0) then the object is either :
• at rest or
• moving at constant velocity

### Questions

1. What is the magnitude of the resultant force that acts on a resting object?
zero
2. An object is moving at a constant velocity of 20ms-1. What is the size of the resultant force that acts on this object?
zero
3. What property of matter keeps an object moving at it's constant velocity?
it's inertia
4. If you are in a moving vehicle and it suddenly stops, you keep moving forward. What property of matter keeps you moving forward?