Physics - module 4

Physics - module 4

1. speed (metre per second, m/s) = distance travelled (metre, m) / time taken (second, s)

2. distance-time graphs

   • the vertical axis on a distance-time graph is the distance travelled from the start
   • the horizontal axis on a distance-time graph is the time taken from the start
   • the steeper the line, the greater the speed of the object
     • gradient = the change in the vertical axis / the change in the horizontal axis

3. velocity-time graphs

   • the vertical axis of the velocity-time graph is the velocity of the object
   • the horizontal axis of the velocity-time graph is the time taken from the start
   • the velocity of an object is its speed in a particular direction
     • this means that if two cars are travelling at the same speed but in opposite directions, they will have different velocities
       • one velocity will be positive and the velocity on the other direction will be negative
     • the steeper the line, the more rapidly the velocity of the object is changing
       • the line sloping downwards ( with a negative gradient) in this graph represents an object that is steadily slowing down
   • an example of a velocity-time graph is a lorry tachograph, tachograph records are circular disks that record the speed of a vehicle, this shows whether the lorry driver has been keeping to the speed limit and taking regular breaks

4. sped-time graphs

   • a speed-time graph tells us how the speed of an object changes over time
     • a horizontal line on a speed-time graph indicates a steady speed
     • the steeper the gradient of the iine, the greater there acceleration (a bigger change in speed in the same time)
       • acceleration = change in speed / tine taken

5. forces

   • forces happen when there is an interaction between two objects, these forces always happen in pairs - when one object exerts a force on another, it always experiences a force in return
     • an interaction pair is when two forces are equal in size and opposite in direction
   • sometimes a force is produced in a response to another force - these are not the same as an interaction pair
   • friction is n example of a force, when two surfaces slide past each other, the interaction between them produces a force of friction

6. momentum = mass of the object x the velocity of the object

   • forces change momentum - the larger the force the more quickly the momentum changes
     • the resultant force is the overall result of all forces acting together
       • when the car is increasing its speed then all these forces add to give a single resultant force forwards

7. momentum (in kg m/s) = mass (in kg) x velocity (in m/s)

   • the size of the change in momentum depends on the size of the resultant force and the time for which the force acts
     • change of momentum (in kg m/s) = resultant force (in Newton, N) x time for which it acts (in s)
   • cars are fitted with front and rear crumple zones, as they gradually deform they increase the amount of time the person takes to come to a stop, this reduces the acceleration and force on the person, so reducing injury from impact

8. equatoons

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