3.1 motion

• what is displacement?

  displacement is a vector quantity. it is the shortest distance from starting point to ending point.
• what is velocity? 


  the rate of change of displacement
• what is average speed? 


  the total distance travelled per unit of time - total distance divided by total time
• what is what is acceleration?

  the rate of change of velocity of an object
• what is instantaneous speed? 


  the instantaneous speed is the speed ( or velocity) at any given moment in time
• what does this graph show?

  it is a displacement - time graph. to find the instantaneous speed at any given time draw a tangent and work out its gradient. the y intercept is equal to initial displacement. a curved line indicated an accelerating object.

  
• what do these graphs show? 


  they are velocity time graphs. gradient is equal to acceleration. y intercept equals initial velocity. a curved line represents non uniform acceleration. area under the graph is equal to displacement.

  
• what do these graphs represent?

  they are acceleration time graphs. the y intercept is the initial acceleration. area under the graph is equal to change in velocity.

  
• what is acceleration due to free fall?

  the acceleration of free fall , g , is defined as: the acceleration of any object in response to the gravitational attraction between the earth and the object.
• what are errors that may occur during free fall experiment?

  Systematic Errors:

  • Residue magnetism after the electromagnet is switched off may cause t to be recorded as longer than it should be

  Random Errors:

  • Large uncertainty in h from using a metre rule with a precision of 1 mm
  • Parallax error from reading h
  • The ball may not fall accurately down the centre of each light gate
  • Random errors are reduced through repeating the experiment for each value of h at least 3-5 times and finding an average time, t
• what is stopping distance?

  stopping distance is braking distance + thinking distance. it is the distance a car travels in the time it takes a car to stop in an emergency.
• what is braking distance?

  distance travelled by the car after the brakes are applied
• what is thinking distance?

  distance travelled by the car from when the driver sees an obstacle to when he responds to it

  thinking distance = reaction time x initial speed
• what is the relationship between thinking distance and speed?

  thinking distance is directly proportional to speed
• what is the relationship between braking distance and speed?

  is proportional to square of the initial speed
• what affects thinking distance?

  initial speed

  alcohol

  tiredness
• what affects braking distance?

  initial speed

  mass of vehicle

  road conditions

  car conditions
• Determining g using light gates

  1. Set up the apparatus, connecting the light gates to a data logger and as close to the electromagnet as possible

  2. Adjust the position of the lower light gate such that the height (h) is 0.75 m, measured using the metre ruler

  3. Turn on the electromagnet and attach the ball bearing

  4. Switch off the electromagnet, and note the time taken for the bearing to fall between the light gates (t) as recorded by the data logger

  5. Reduce h by 0.05 m by moving the lower light gate upwards and repeat the above two steps, reducing h by 0.05 m each time down to 0.25 m

  6. Repeat the experiment twice more to find mean values of t for each value of h

  7. Place a pad at the bottom to prevent ball from bouncing

  8. Place a counterweight on the base of the stand so that it does not fall over