Acceleration The Space Shuttle accelerates off the launch pad at 50m/s/s. Every second the Shuttle increases its speed by 50m/s. From a standing start it increases its speed from zero to 50m/s in the first second of flight. Two seconds into its flight and its speed is now 100m/s. The rate at which the speed of an object changes is called acceleration. If we were to look at the speed-time graph of an object in motion the slope of the graph would represent the acceleration. The slope of the speed-time graph represents the magnitude of the acceleration. The greater the slope the greater the acceleration. Deceleration (negative acceleration) is represented by a graph with a negative slope. Zero acceleration is represented by a straight line on the speed-time graph. This indicates a constant speed and so no acceleration is present. Look at the speed-time graph on the left. Notice that the object accelerates between 0 and 5 seconds. The acceleration can be calculated by calculating the slope of the graph. Slope = acceleration = Rise/run = 10ms/5s = 2m/s/s. So the speed is increasing by 2m/s every second. Between 5 and 10 seconds the speed is constant and therefore the acceleration is zero. The object once again accelerates between 10 and 13 seconds. the acceleration is calculated. Slope = acceleration = Rise/run = 20ms/3s = 6.7m/s/s. So the speed is increasing by 6.7m/s every second. Between 13 and 16 seconds the object is accelerating but at a lesser rate. Slope = acceleration = Rise/run = 2ms/3s = 0.67m/s/s. So the speed is increasing by 0.67m/s every second. During the last 6 seconds a strong deceleration occurs. Slope = deceleration = Rise/run = 22ms/6s = 3.7m/s/s. So the speed is decreasing by 3.7m/s every second.