Describing the motion of an object is occasionally hard to do with words. Sometimes graphs help make motion easier to picture, and therefore understand.
Remember:
• Motion is a change in position measured by distance and time.
• Speed tells us the rate at which an object moves.
• Velocity tells the speed and direction of a moving object.
• Acceleration tells us the rate speed or direction changes.
SPEED-TIME GRAPHS
Speed-Time graphs are also called Velocity-Time graphs.
Speed-Time graphs look much like Distance-Time graphs
Be sure to read the labels!!
Time is plotted on the X-axis. Speed or velocity is plotted on the Y-axis.
A straight horizontal line on a speed-time graph means that speed is constant. It is not changing over time.
A straight line does not mean that the object is not moving!
This graph shows increasing speed.
The moving object is accelerating.
This graph shows decreasing speed.
The moving object is decelerating.
What about comparing two moving objects at the same time?
Both the dashed and solid line show increasing speed.
Both lines reach the same top speed, but the solid one takes longer.
The dashed line shows a greater acceleration.
Summary:
A speed - time graph shows us how the speed of a moving object changes with time.
• The steeper the graph, the greater the acceleration.
• A horizontal line means the object is moving at a constant speed.
• A downward sloping line means the object is slowing down.
