# Physics P3 Changing Speed

Created by AP.

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• Created by: A.P
• Created on: 19-01-13 12:48
• Changing Speed
• Speed-Time Graphs
• A change in 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.
• The area under a speed-time graph is equal to the distance travelled.
• In the diagram, OA shows acceleration, AB shows moving at a constant speed, BC shows deceleration CD shows no movement, DE shows acceleration and EF shows moving at a constant speed, although slower than before.
• Untitled
• Acceleration
• The formula for measuring acceleration is...
• change in speed (or velocity) / time taken
• Acceleration is measured in metres per second squared (m/s2). A negative acceleration shows the car is decelerating.
• Changing 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 going in opposite directions, or the difference between their individual velocities if they are going in the same direction.
• Circular Motion
• Any object moving along a circular path moves at a tangent to the circle, or arc of the circle.
• A vehicle may go around a roundabout at a constant speed but it is accelerating. This is because its direction of travel is changing; it's not going in a straight line.
• The driver needs to apply a force towards the centre of the roundabout to change direction. This gives the vehicle an acceleration directed towards the centre of the roundabout.