Speed-time graphs
Speed-time graphs are very useful when describing the movement of an object.
We can use them to determine whether or not the object is moving at any point in time. We can also use them to see what The distance travelled in a fixed time period, usually one second. the object is travelling at that point in time.
Using data from the graph, we can calculate any The rate of change in speed (or velocity) is measured in metres per second squared. Acceleration = change of velocity ÷ time taken., the change in speed and the change in time.
We can also use graphs to calculate Numerical description of how far apart two things are. For example, the distance from Edinburgh to Glasgow is approximately 50 miles. travelled. The area under a speed-time graph represents the distance travelled.
This is a velocity time graph of an object moving in a straight line due North.
The displacement of this object is the area of the velocity time graph. To calculate the displacement we need to calculate the area. This means dividing the “area” into a series of triangles and rectangles that allows us to determine the overall displacement. In this case the displacement is 118m.
In this case the object starts from rest, accelerates for 6s. It stays at a constant velocity of 9ms-1 for 4s then slows down to 5ms-1 in a further 4s. I travels at 5ms-1 for another 4s then rapidly slows down and comes to rest.
A Parallel to the ground. line on a speed-time graph represents a constant speed.
A sloping line on a speed-time graph represents an acceleration. The sloping line shows that the speed of the object is changing. The object is either speeding up or slowing down.
The steeper the slope of the line the greater the acceleration. If the line slopes downwards from left to right on the graph, this means that the object is slowing down. This motion is sometimes referred to as a 'Slowing down or negative acceleration, eg the car slowed down with a deceleration of 2 ms⁻².'. However remember that a 'deceleration' is really just a special kind of 'acceleration'. It is an acceleration where the speed of the object is decreasing with time.
