If the graph is curved, there are a number of ways of estimating the area (see trapezium rule below). The distance travelled can be calculated by finding the area under a velocity-time graph. If the graph is curved, this can be done by drawing a chord and finding its gradient (this will give average velocity) or by finding the gradient of a tangent to the graph (this will give the velocity at the instant where the tangent is drawn).Ī velocity-time graph has the velocity or speed of an object on the vertical axis and time on the horizontal axis. The velocity can be calculated by finding the gradient of the graph. These have the distance from a certain point on the vertical axis and the time on the horizontal axis. Acceleration is therefore the rate of change of velocity (change in velocity / time) and is measured in m/s².Ī car starts from rest and within 10 seconds is travelling at 10m/s. If the velocity decreases it is said to be decelerating. When the velocity (speed) of a moving object is increasing we say that the object is accelerating. Velocity is the speed of a particle and its direction of motion (therefore velocity is a vector quantity, whereas speed is a scalar quantity). Therefore distance travelled = 10 × 180 = 1800m = 1.8km Now rearrange the first equation to get distance = speed × time. If a car travels at a speed of 10m/s for 3 minutes, how far will it travel?įirstly, change the 3 minutes into 180 seconds, so that the units are consistent. So we divide by 60, not multiply to get a smaller number. If you think about it, in 1 minute, the object is going to travel less distance than in an hour. Often people have problems working out whether they need to divide or multiply by a certain number to change the units. In line (1), we divide by 60 because there are 60 minutes in an hour.
#Find average speed on a graph how to
The following is an example of how to change the units: m/s, m and s or km/h, km and h), change the units before starting, as above. In calculations, units must be consistent, so if the units in the question are not all the same (e.g.
If speed does change, the average (mean) speed can be calculated: For example speed could be measured in m/s, distance in metres and time in seconds. Remember, when using any formula, the units must all be consistent. The following is a basic but important formula which applies when speed is constant (in other words the speed doesn't change): This section covers travel graphs, speed, distance, time, trapezium rule and velocity.
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