You may be asked to identify certain aspects of a motion graph.
The graph can be either one of these:
- Velocity – Time Graph
- Displacement – Time Graph
- Acceleration – Time Graph
Velocity – Time Graph
The velocity-time graphs could have the following components:
- Constant Velocity, shown by the green line on the graph
- Constant Acceleration , shown by the blue line on the graph
- Constant Deceleration, shown by the red line on the graph
- Area under graph = total distance covered
The first three points are straight forward.
The fourth point may be slightly tricky. You may be asked to calculate the total distance covered by a vehicle.
The graph shown above is shaped like a trapezium. You will be given the values on the graph. You can then use the area of trapezium formula to find the area under the graph. This will give you the total distance travelled by the vehicle.
The graphs can be of different shapes too, not just trapezium-shaped.
Displacement – Time Graph
The displacement – time graphs could have the following components:
- Stationary phase. This is shown by the green line on the graph. Since, displacement is constant, the body is not in motion. Therefore, it is at rest.
- Constant positive velocity.This is shown by the blue line on the graph. The displacement is increasing proportionally. Therefore, the velocity is increasing at a constant rate.
- Constant negative velocity. This is shown by the red line on the graph. The displacement is decreasing proportionally. Therefore, the velocity is decreasing at a constant rate.
Also, it is important to note that displacement becomes zero. Since displacement is a vector quantity, this shows that the body returns to its original starting position.
- Acceleration. This is shown by the orange line on the graph.The displacement is increasing at an increasing rate. Therefore it must be accelerating.
- Deceleration. This is shown by the purple line on the graph.The displacement is decreasing at an decreasing rate. Therefore it must be decelerating.
- The gradient of any line on the graph give us the value of the velocity.
Acceleration – Time Graph
There is not much they can ask you about acceleration-time graphs.
- The green line shows constant acceleration. This means that the body is accelerating at a constant rate.
- The dashed line shows that the body begins to move at a constant velocity. Since the velocity becomes constant, i.e. velocity remains same, acceleration suddenly drops to zero.