Forces and Acceleration

• Acceleration


  A measure of how quickly an object speeds up, slows down or changes direction
• Calculating acceleration


  acceleration = change in velocity/time taken
• Acceleration (a)


  Measured in metres per second squared (m/s(2))
• Change in velocity (v)

  Found by subtracting initial velocity from final velocity (v-u), measured in metres per seconds (m/s)
• Time (t)


  Measured in seconds (s)
• When an object slows down

  The change in velocity is negative, so it has a negative acceleration
• Calculating acceleration using equation


  (final velocity)2 - (initial velocity)2 = 2 x acceleration x distance
• Final velocity (v)


  Measured in metres per second (m/s)
• Initial velocity (u)


  Measured in metres per second (m/s)
• Distance (s)


  Measured in metres (m)
• Velocity-Time Graphs


  . 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
• Newton's 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
• Newton's Second Law


  1. If the resultant force is doubled, the acceleration will be doubled

  2. If the mass is doubled, the acceleration will be halved
• Force (F)


  Measured in newtons (N)
• Mass (m)


  Measured in kilograms (kg)
• Acceleration (a)


  Measured in metres per second squared (m/s2)
• Mass


  A measure of inertia
• Mass


  Describes how difficult it is to change the velocity of an object
• Inertial mass


  Given by the ratio of force over acceleration (m=F/a)
• Mass


  • The larger the mass, the bigger the force needed to change the velocity
• Force = mass x acceleration
• F = ma
• Investigate the effect of varying the force and/or the mass on the acceleration of an object

  1. Set up the equipment

  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
• 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 innacurate
• Independent variable


  The force or the mass
• Control variable


  Kept the same. In this case, the force if the mass is changed or the mass if the force is changed
• What is a key point to remember about calculating a mean?

  . Calculating a mean helps to reduce the effect of random errors

  . A result that is accurate is close to the true value