# P3 - B

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• Created by: zoolouise
• Created on: 02-06-15 19:01
• Changing speed
• Speed-time graphs
• A change of speed per unit time is called acceleration.
• If the speed is increasing, the object is accelerating. If the speed is decreasing, the object is decelerating.
• Acceleration
• Acceleration = change in speed (or velocity) / time taken
• Acceleration is measured in metres per second squared.
• A negative acceleration shows the car is decelerating.
• Relative velocities
• Velocity is a vector, it has both size (speed) and direction
• When two cars are moving past each other their relative velocity is ;
• The sum of their individual velocities if they are moving in opposite directions
• The different of their individual velocities if they are moving in the same direction.
• Circular motion
• A vehicle may go around a roundabout at a constant speed but it's accelerating.
• This is because the direction of travel is changing, it isnt going in a straight line.
• The driver needs to apply force towards the center of the roundabout to change direction. This gives the vehicle an acceleration directed towards the centre of the roundabout.
• Any object moving along a circular path moves at a tangent to the circle, or arc of a circle.