Forces and Acceleration

• The gradient of a velocity-time graph can be used to find the acceleration of an object.

  The total distance travelled is equal to the area under the graph.
• Required Prac: Sample Method

  1. Set up the equipment as shown.
  2. Release the trolley and use light gates or a stopwatch to take the measurements needed to calculate acceleration.
  3. Move 100g (1N) from the trolley onto the mass holder.
  4. Repeat steps 2 and 3 until all the masses have been moved from the trolley onto the mass holder.

  If investigating the mass, keep the force constant by removing a mass from the trolley but not adding it to the holder.
• RP: Considerations, Mistakes and Errors

  • When changing the force it is important to keep the mass of the system constant. Masses are taken from the trolley to the holder. No extra masses are added.
  • Fast events often result in timing errors. Repeating results and finding a mean can help reduce the effect of these errors.
  • If the accelerating force is too low or the mass too high, then frictional effects will cause the results to be inaccurate.
• RP: Hazards and Risks

  • The biggest hazard in this experiment is masses falling onto the experimenter's feet. To minimise this risk, masses should be kept to the minimum needed for a good range of results.
• RP: Variables

  • The independent variable is the force or the mass.
  • The control variable is kept the same.In this case, the force if the mass is changed or the mass if the force is changed.
• Newtons Second Law:

  The acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of the object, i.e.

  • if the resultant force is doubled, the acceleration will be doubled
  • if the mass is doubled, the acceleration will be halved.
• Mass is a measure of inertia.

  It describes how difficult it is to change the velocity of an object.

  This inertial mass is given by the ratio of force over acceleration.

  The larger the mass, the bigger the force needed to change the velocity.