Distance-Time and Velocity-Time Graphs _ GCSE Physics

When were talking about motion, it can be very useful to draw a graph. If you're moving in a straight line, a graph that's useful is a distance-time graph; this is where you have distance on the Y-axis and time on the X. If we mark this as the starting point and start walking at a steady speed of 2m/s, then we can plot this on the graph and draw a straight line between the points. If we decide to stop the line would be flat, then if we return to our original position the line slopes back to the origin of the graph. You can use the steepness of the slopes to work out your speed. If the line is very steep then you're moving fast but if you're moving slowly then the graph will have a gentler slope. You can then use the numbers on the axis to work out the actual speed you were traveling. The equation for speed is distance over time, so all you have to do is read the numbers, if you travelled 20m in 5 seconds then your speed will be 4m/s. If you want to work out how fast an apple falls to the ground then a distance-time graph won't do because the pull of gravity causes it to accelerate. Instead we can use a velocity time graph. In this case the slope of the graph tells us that an object is accelerating. If the line is straight then the acceleration is constant and if it's curved then the acceleration is changing. You can work out the acceleration of an object by dividing the change in velocity by the time it took to fall. If the graph shows a straight horizontal line, the object is travelling at a constant speed. When the graph starts to slope back to the origin, it means the object is decelerating. For instance when the apple hits the floor, the graph would show a very steep line. You can also find the distance you've travelled by working out the area under the graph. It's as easy as working out the areas of squares, triangles and trapeziums and hence how far you've travelled.