PHYSICS - Forces - Average Speed

Take a look at this person running a race. You might already know that we can calculate his speed, (1), by dividing the distance the man has travelled, say 100m (2), by the time it has taken him, say 20 seconds (3). So his speed = distance divided by time, which is 100 divided by 20, or 5 metres per second. However, this assumes that the man is running at a constant speed for the entire race. What does that mean? Watch this video to find out.