Distance - Time graphs

Distance - Time graphs

Distance - This length between any two points.

It is measured in metres.

Example:

A ______________________ B

Distance between Point A and B is 10 m

Distance

• Distance is length between any two points.

  It is measured in metres.

  Example:

  A ______________________ B

• Distance between Point A and B is 10 m

Time

• Time is duration of an event.

  Time is measured in seconds

  
  

  Example:

  An online quiz question takes an average of 7 seconds.

Speed

Speed is the rate of change of distance with time.

It is measured in metres per second, m/s

Example

Calculate the speed of a car that took 5 seconds to cover 100 m.

Soln

Speed = d/t = 100 m/5 s = 20 m/s

Distance - Time graph

Finding Speed

• The speed of an object is given by the gradient of the line

Distance - Time graphs

• A horizontal line means stationary.

• A straight line means constant speed.

• If the gradient increases the object is speeding up (accelerating).

• If the gradient decreases the object is slowing down (decelerating).

• If the line is going down, the object is moving backwards.

Exam Tip

• When you come across any graph, look carefully at what is plotted on each axis and think for a while about what the graph is showing you.

• Distance-time graphs are also known as position-time graphs or displacement-time graphs. Don’t be fooled by these different names: They describe the same kind of things.

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Speed

• The Relationship between average speed, distance moved and time taken

• Speed (measured in metres per second) is the distance moved by an object each second.

• The average speed of an object is given by the equation:

• Average speed = distance moved / time taken

• You can rearrange the equation with the help of the formula triangle:

You can rearrange the equation with the help of the formula triangle:

Use the formula triangle to help you rearrange the equation

Exam Tips

• Use the units of speed (metres per second – distance divided by time) to help you remember the formula.

• The equation is for average speed, but the speed at a specific moment might be higher or lower.

Example 1

Calculate the average speed of a car that traveled 50 m in 3.9 s.

Example 1 - Solution

Calculate the average speed of a car that traveled 50 m in 3.9 s.

Solution

Average speed = Distance moved / time taken

Average speed = 50 m / 3.9 s

Average speed = 12.8 m/s

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