newton's first law: inertia

what is inertia?

the tendency of an object to stay at rest or continue in uniform motion

what sort of objects have high inertia?

• high mass (e.g. bowling ball, wrecking ball)

• hard to move/stop moving (trolley)

what is Newton’s first law?

if the resultant force is 0, the object stays at rest if it is stationary, or keeps moving at a constant speed in the same direction (inertia)

how do the forces interact when the object moves at a constant velocity?

the resistive forces (air resistance and friction) and the driving (motive) force are balanced

when will the velocity (speed/direction) of a vehicle change?

if the forces are no longer balanced

what is velocity?

travelling at a constant speed in the same direction

how does a space probe travel and why?

at a constant velocity: there are no forces at all on it (no air resistance or gravity)

how does applying brakes effect the car?

friction is increased to give a resultant force and decelerates the car

how does a car’s direction change?

the sideways friction between the tyres and track provides a result force

what is inertial mass?

• the measure of how difficult it is to change the velocity of an object

• the ratio of force over acceleration