Motion

• Define speed and calculate the average speed from total distance / total time

The speed of an object is the distance it travels per unit of time. This formula is one of the most fundamental formulae you need to know for this course.

• Distinguish between speed and velocity.

Speed: 

Speed is something which we describe as being scalar. This means that speed measures how fast an object is going - regardless of what direction the object is moving in.

Scalar only has a magnitude (value (in this case, the value of how fast you're going)), NOT a direction.

Velocity:

We describe velocity as being a vector. A vector is something which takes into account both magnitude AND direction. The velocity of an object considers which direction it is going as well as how fast it is moving.

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

  • Recognise from the shape of a speed/time graph when a body is: at rest, moving with constant speed, moving with changing speed.

                       Speed/Time Graph

 When looking at graphs for moving objects, it is extremely important that we consider the axes. In the graph above, the axes are speed and time (i.e. a speed-time graph).  The green part of the graph shows how the speed of the object is increasing. Since the gradient is constant, we know that the object has a constant acceleration (i.e. its speed is increasing at a constant rate). 
The orange part of the graph shows where the object has a constant speed. The object is still moving, but its speed is not increasing or decreasing. 
The blue part of the graph shows where the speed is decreasing. The same thinking applies here as to the green part of the graph. As the value of the speed is approaching zero (the  gradient/slope is negative), we can deduce that the acceleration is decreasing. In other words, the object is going from having a high speed to no speed (deceleration). As the gradient has a constant value, the object has a constant deceleration. 

You can see when an object is moving with CHANGING speed when the line in a speed-time graph is NOT constant (not straight) but curved/squiggly. 

                 Distance/Time Graph

In the graph above, we can see a distance-time graph. In the green part of the graph, the object is moving away from its original position (it is gaining displacement). The gradient is constant which means that the speed is constant, too. The object is increasing in distance at a constant rate. Therefore, it has a constant speed (no acceleration or deceleration). 

In the orange part of the graph, the object is stationary. The object is not gaining or losing any distance - it is "standing still" (stationary). 

In the blue part of the graph, the object is moving back towards its original position. As the gradient is constant, the speed is constant. 

Technically, it would be more accurate to refer to the movement of an object in terms of velocity and displacement. 

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

In linear motion, the way to calculate acceleration is through using the following formula: 

Acceleration = Change in speed / time. 

When an object is moving, you can determine its acceleration (how fast its speed increased / the rate of increase of speed) through dividing the change of its speed by the time taken (how long it took for change of speed to happen). 

You can rearrange this formula to find the speed or time depending on which values are available in the question. 

• Recognise motion for which acceleration is not constant.

In real-life, it is incredibly unlikely that one would be able to drive a car (for example) and speed up/slow down at an exact, constant rate. The acceleration of an object is likely to change around a bit.

When the acceleration is not constant, the gradient is NOT constant.

• Calculate the area under a speed/time graph to work out the distance travelled for motion with constant acceleration.
• Demonstrate a qualitative understanding that acceleration is related to changing speed.

You can calculate the DISTANCE TRAVELLED for an object through calculating the area under its speed-time graph. 

Acceleration is all about the changing of speed. When speed increases, we call it acceleration. When speed decreases, we call it deceleration. 

Acceleration is the measure of the change of speed of an object per unit time, more specifically, the velocity of the object.