Motion

Distance -time graphs, velocity and acceleration, velocity - time graphs, and using graphs

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Distance - Time Graphs

  • We can use graphs to help us describe the motion of an object.
  • A distance-time graph shows us the distance of an object from a starting point (y-axis) against the time taken (x-axis)
  • The speed of an object is the distance travelled each second
  • The graident of the line on a distance-time graph represents the speed. The steeper the graident the greater the speed.
  • If an object is stationary, the line on a distance-time graph is horizontal
  • If an object is moving at a constant speed, the line on a distance-time graph is a straight line that slopes upwards.
  • We can calculate the speed of an object using the equation:

     Speed in metres per second, m/s = distance travelled in metres, m

                                                             time taken in seconds, s

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Velocity and Acceleration

  • The velocity of an object is its speed in a given direction.
  • If the object changes direction it changes velocity, even if its speed stays the same.
  • If the velocity of an object changes, we say that it accelerates.
  • We can calculate acceleration using the equation:

                     a = v - u

                             t

a = acceleration ( m/s )

v = final velocity (m/s)

u = initial velocity (m/s)

t = time taken for the change (s)

If the value calculated for acceleration is negative, the body is decelerating. A deceleration is the same as a negative acceleration.

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Velocity - Time Graphs

  • A velocity - time graph shows the velocity of an object (y-aixs) against the time taken (x-axis)
  • The graident of the line on a velocity-time graph represents acceleartion.
  • The steeper the graident, the greater the acceleration
  • If the line on a velocity-time graph is a horizontal line, the acceleratiuon is zero. Therefore the object is travelling at a steady speed.
  • If the graident of the line is negative, the object is decelerating
  • The area under the line on a velocity-time graph represents the distance travelled in a given time. 
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Using Graphs...

key points:

  • The speed of an object is given by the graident of the line on its distance-time graph
  • The acceleration of an object is given by the graident of the line on a velocity-time graph
  • The distance travelled by an object is given by the area under the line of its velocity-time graph.
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Comments

Miss KHP


Really helpful for all exam boards as it does come up in the exam but check your specification to see what exam it comes up in. For example, for AQA, this comes up in Additional Science (usually taken in year 11).

If you are stuck on this topic, use these notes to help you and then test yourself to check your progress.

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