The velocity of an object is its speed in a particular direction.
This means that two objects could be travelling at the same speed but have different velocities. For example, two cars are travelling at 30 m/s along the same road but in opposite directions:
The opposite signs show that they are travelling in opposite directions.
If two objects are moving in parallel their relative velocity can be calculated.
For example, two cars are moving in the same direction along a road. Car A is travelling at +30 m/s and Car B is travelling at +20 m/s. Their relative velocity is 30 – 20 = +10 m/s.
If the two cars are moving in opposite directions, the velocity of Car A is +30 m/s and the velocity of Car B is –20 m/s. Their relative velocity is 30 –(–20) = 30 + 20 = +50 m/s.
Acceleration is a change in velocity. This means that an object accelerates if:
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