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Forces and Motion

What are Distance, Displacement, Speed and Velocity?

What is Distance?

Distance is a measure of how far an object has travelled
from its starting point, or how far away it is.
Distance is the same as length and is measured in metres.

What is the Difference between Distance and Displacement?

Displacement (like distance above) is also a measure of
how far an object has travelled from its starting point
but displacement also tells you the direction of the object.
Distance is a scalar and displacement is a vector.

What is Speed?

Speed is a measure of how fast an object is moving.
It is measured in metres per second, written as m/s.

Speed = Distance ÷ Time.

What is Velocity?

Velocity is similar to speed.
It is also a measure of how fast an object is moving
and is measured in m/s.

Velocity = Distance ÷ Time.

If an object is not moving then it is called stationary.
The speed or velocity of a stationary object is zero.

What is the Difference between Velocity and Speed?

The difference between velocity and speed is that
velocity is speed in a certain direction.
Speed is a scalar and velocity is a vector.

If an object is moving in a straight line, then its speed and velocity
will be the same.
If the moving object stays at the same speed but changes direction
then we say that
the velocity has changed (because the direction has changed)
but the speed has stayed the same.

If the velocity in one direction is positive
(for example, forwards at 10 m/s)
then the velocity in the opposite direction is negative
(for example, backwards at -10 m/s).

In most of the examples of motion that you will come across,
the object will be moving in a straight line.
In this case, we will use the word velocity rather than speed
(see the next page for calculations).

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