Speed

• Speed is the rate at which an object's position changes, measured in meters per second.

• The formula for speed is Speed = Distance / Time.

• There is more than one way to determine the speed of a moving object : The total distance travelled between two points

• The Key equation of time is Avg Speed = Total distance traveled / total time taken

Example for time formula

• We can use the equation for speed in the definition when an object is travelling at a constant speed. If it travels 10 metres in 1 second, it will travel 20 metres in 2 seconds. Its speed is 10 m/s. I got 10 m/s as i divided 20/2 and 10/1.

• We cannot say whether it was travelling at a steady speed, or if its speed was changing. For example, you could use a stopwatch to time a friend cycling over a fixed distance, for example, 100 metres. Dividing distance by time would tell you their average speed, but they might have been speeding up or slowing down along the way.

Units of measurement and time

• Shows the different units that may be used in calculations of speed. SI units are the standard units used in physics. The units m/s (metres per second) should remind you that you divide a distance (in metres, m) by a time (in seconds, s) to find speed.

Table for si units and other unit of other quantity

Questions

• What was Usain Bolt’s average speed when he achieved his 100 m world record of 9.58 s in 2009?

  
  

• A cheetah runs 100 m in 3.11 s. What is its speed?

Answers

• For finding the speed we need to divide distance by time , distance = 100 m and time = 9.58 s. Speed = 100 / 9.58 = 10.438 m/s.

• To find the speed we have to divide distance by time , S = 100 / 3.11 = 32.154.

Activity

• Which train has the highest average speed?

• Which train has the lowest average speed?

Answers

• Train C

• Train B