P9 Motion
Speed and Distance-Time Graphs
If an object is moving at a constant speed, the distance-time graph is a straight line that slopes upwards
The gradient of a distance-time graph for an object represents the object's speed
If an object is stationary, the distance-time graph is a horizontal line
Velocity = Speed / Time
Velocity and Acceleration
A scalar is a physical quantity that has a magnitude only and does not have a direction
Acceleration = Change in velocity / time
A vector is a physical quantity that has a direction as well as a magnitude
Deceleration is the change of velocity per second when an object slows down
Velocity is speed in a given direction
Velocity-Time Graphs
If a velocity-time graph is a horizontal line, the acceleration is zero
A positive gradient on a velocity-time graph represents positive acceleration, a negative gradient represents deceleration
The gradient of the line on a velocity-time graph represents acceleration
A motion sensory linked to a computer can be used to measure velocity changes
The area under the line on a velocity-time graph represents distance travelled
Analyzing Motion Graphs
The distance traveled by an object is given by the area under the line on its velocity-time graph
The speed at any instant in time, of an object moving at changing speed is given by the gradient of the tangent to the line on its distance-time graph
The acceleration of an object is given by the gradient of the line on its velocity-time graph
The speed of an object moving at constant speed is give by the gradient of the line on its distance-time graph