PAG: Investigating Force & Acceleration (OCR Gateway GCSE Physics: Combined Science)

• Two experiments are described which investigate the relationship between force and acceleration

Equipment List

• Resolution of measuring equipment
  • Metre ruler = 1 mm
  • Stopwatch = 0.01 s

Experiment 1: Investigating the Effect of Force on Acceleration

Aim of the Experiment

• The aim of this experiment is to investigate the effect of varying force on the acceleration of an object of constant mass

Variables

• Independent variable = force, F
• Dependent variable = acceleration, a
• Control variables:
  • Mass, m

Method

Force and acceleration apparatus setup

1. Use the metre ruler to measure out intervals on the bench, e.g. every 0.2 m for a total distance of 1 m. Draw straight lines with pencil or chalk across the table at these intervals
2. Attach the bench pulley to the end of the bench
3. Tie some string to the toy car or trolley
4. Pass the string over the pulley and attach the mass hanger to the other end of the string
5. Make sure the string is horizontal (i.e. parallel to the bench) and is in line with the toy car or trolley
6. Hold the toy car or trolley at the start point
7. Attach the full set of masses (total = 1.0 N) to the end of the string
8. Release the toy car or trolley at the same time as you or a partner starts the stopwatch. Press the stopwatch (in lap mode) at each measured interval on the bench and for the final time at 1.0 m
9. Record the results in the table and repeat step 8 to calculate an average time for each interval
10. Repeat steps 6-9 for decreasing weights on the weight hanger, e.g. 0.8 N, 0.6 N, 0.4 N, and 0.2 N. Make sure you place the masses that you remove from the weight stack onto the top of the car, using the Blu-tac, each time you decrease the weight

• A possible results table is illustrated as an example below:

Analysis of Results

• Use the table of results to determine the average speed of the trolley between intervals
• Use the distance between each interval (0.2 m) and the average time it takes for the toy car or trolley to travel that distance to calculate the average speed per interval
  • This is done using the equation:

• Compare the average speed between the first and last intervals for different weights
• Use the equation below to calculate the acceleration between the first and the last intervals:

• Do this for each different weight, comparing how the acceleration varies

Experiment 2: Investigating the Effect of Mass on Acceleration

Aim of the Experiment

• The aim of this experiment is to investigate the effect of varying mass on the acceleration of an object produced by a constant force

Variables

• Independent variable = mass, m
• Dependent variable = acceleration, a
• Control variables:
  • Force, F

Method

1. Use the metre ruler to measure out intervals on the bench, e.g. every 0.2 m for a total distance of 1 m. Draw straight lines with pencil or chalk across the table at these intervals
2. Attach the bench pulley to the end of the bench
3. Put a 200 g mass on the car
4. Tie some string to the toy car or trolley
5. Pass the string over the pulley and attach the mass hanger to the other end of the string
6. Make sure the string is horizontal (i.e. parallel to the bench) and is in line with the toy car or trolley
7. Select a mass to put on the mass hanger that will gently accelerate the car along the bench. This provides the constant force on the car or trolley and will not change
8. Hold the car at the start point
9. Release the car at the same time as you or a partner start the stopwatch. Press the stopwatch (in lap mode) at each measured interval on the bench and for the final time at 1.0 m
10. Record the results in the table and repeat step 8 to calculate an average time for each interval
11. Repeat steps 6-9 for increasing mass on the car, e.g. 400 g, 600 g, 800 g and 1000 g

• A possible results table is illustrated as an example below:

Analysis of Results

• As in Experiment 1, use the table of results to determine the average speed of the trolley between intervals
• Use the distance between each interval (0.2 m) and the average time it takes for the toy car or trolley to travel that distance to calculate the average speed per interval
  • This is done using the equation

• Compare the average speed between the first and last intervals for different weights
• Use the equation below to calculate the acceleration between the first and the last intervals:

• Do this for each different mass on top of the toy car or trolley, comparing how the acceleration varies

Evaluating the Experiments

Systematic Errors:

• In Experiment 1, ensure any mass removed from the mass hanger are transferred to the toy car or trolley
  • This is to ensure the total mass of the system remains constant

Random errors:

• A main cause of error in this experiment is the measurements of time
  • Ensure to take repeat readings when timing intervals and calculate an average to keep this error to a minimum

• Start the toy car by releasing it, allowing it to accelerate under the force of the masses attached by the string
  • Ensure not to give it a 'push'

Safety Considerations

• Don't stand directly beneath the mass hanger, in case any masses become loose and fall off the stack
  • Place a crash mat underneath the mass hanger just in case this happens