Physics Unit 1: Motion

source

Unit 1 Motion

1. Define speed and calculate speed from total distance / total time.

Speed is the rate of how fast something travels, measured by how far it has travelled in how much time. The equation we use to calculate speed is:

speed = distance / time

2. Distinguish between speed and velocity. 

While speed only measures how fast something travels, velocity measures how fast something travels in a given direction. 

3. Plot and interpret a speed/time graph and a distance/time graph.

First up is a distance/time graph:

source

The blue line and first third of the red line represent a steady speed as they go up in straight lines without and changes. The second third of the red line shows that the object is stationary; you can tell because they have not changed their distance but time is passing. The last third of the red line shows the object returning to its start. 

Now a speed/time graph:

source

The blue line and first third of the red line show constant acceleration. The second third of the red line shows constant speed, as the speed is not changing but time is passing. The last third of the red line shows constant deceleration, because the object's speed is decreasing. 

4. Recognise from the shape of a speed/time graph when a body is 

• at rest, 

• moving with constant speed, 

• moving with changing speed.

source

5. Recognise linear motion for which the acceleration is constant and calculate the acceleration.

By finding the gradient of the line, we can find out if the acceleration is constant. The equation for this is:

acceleration  = change in velocity / time taken

To figure out the change in velocity, you deduct the initial velocity from the final velocity. 

6. Recognise motion for which the acceleration is not constant.

When this is plotted out onto a graph, the line will not be consistent, representing non-constant acceleration.

source

7. Calculate the area under a speed/time graph to work out the distance travelled for motion with constant acceleration. 

To do so, we need to find the gradient of the graph using the rise and the run. The rise is how much the steep rises from its starting position, and the run is how far it travels horizontally from its starting position. 

source

For example, we take random x,y points from the graph above: 4, 20. To find the area, we calculate the area of a triangle, as the shape of the rise/run form a triangle: (4 seconds x 20 meters/second) / 2 = 40 meters. 

8. Demonstrate a qualitative understanding that acceleration is related to changing speed. 

Acceleration is the rate of which an object changes speed, so when a speed changes, we assume that the acceleration has either increased or decreased.