Physics REVISION – Speed, Velocity and Acceleration A Distance/Time graph shows how far an object travels over time. The speed of the object is determined by the gradient of the line. The STEEPER the line the faster an object is going. A horizontal line shows the object is stationary while a curved line demonstrates an acceleration or deceleration object. A Speed/Time graph shows how fast an object is going at any given point in it’s journey. The area under the graph determines the total distance an object travels where as the gradient shows the rate of acceleration of the object. A straight line shows constant acceleration. The STEEPER the line the faster the rate of acceleration of the object. A horizontal line shows a steady speed while a curved line demonstrates an varying rate of acceleration or deceleration object. An object at REST would have no velocity so on a Time/Velocity Graph with show O and would be a line on the X-axis

Physics REVISION – Speed, Velocity and Acceleration Speed = Distance / Time Units include m/s, m.p.h and km/hr Acceleration = Change in velocity / time taken Units are m/s2 Acceleration can be a negative number (this shows deceleration) Speed is a scalar and is simply a number e.g 30 m/s where are Velocity is a vector and has direction e.g 30m/s to the west. If gravity is the only force acting on an object, then we find the object will accelerate at a constant rate of 9.8m/s2 down toward the center of the Earth (this is often rounded to 10m/s2). A straight line on a Speed/Time graph shows constant or uniform acceleration. A curved line shows non-uniform acceleration. A stone is dropped from a great height. There is no initial velocity therefore no air resistance and the stones accelerates at the rate of gravity, g. As the velocity increases so does the air resistance. Eventually the velocity and air resistance reach a maximum and the stone stops acceleration – this is terminal velocity. For example - A skydiver jumps out of a plane and their velocity increases rapidly because they accelerate due to gravity. As they fall air resistance builds up. They are still accelerating but at a lower rate meaning their velocity increases less per second than before. Eventually the force due to gravity equals the air resistance meaning there is no acceleration. The Skydiver has reach the Terminal (Final Velocity). The whole process repeats again when the parachute opens. This time the velocity of the skydiver rapidly decreases (deceleration) due the increase in air resistance, gravity continues to act on the them slowing the rate of deceleration until the forces are equal and they reach a second Terminal velocity meaning no further deceleration or drop in velocity.

Useful information from Distance/Time graphs and Speed/Time graphs