# 5.7.3 Required Practical: Investigating Force & Acceleration

### Required Practical 7: Investigating Force & Acceleration

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

#### 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 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. Pass the string over the pulley and attach the mass hanger to the other end of the string
4. Make sure the string is horizontal (i.e. parallel to the bench) and is in line with the toy car or trolley
5. Hold the toy car or trolley at the start point
6. Attach the full set of weights (total = 1.0 N) to the end of the string
7. 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
8. Record the results in the table and repeat step 7 to calculate an average time for each interval
9. Repeat steps 5-8 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
• 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

#### 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. 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. Select a weight to put on the weight hanger that will gently accelerate the car along the bench. This provides the constant force on the car or trolley and will not change
7. Hold the car at the start point
8. 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
9. Record the results in the table and repeat step 7 to calculate an average time for each interval
10. Repeat steps 5-8 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
• 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:

• Experiment 1: ensure any weights removed from the weight 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 weights attached by the string
• Ensure not to give it a ‘push’

#### Safety Considerations

• Don’t stand directly beneath the weight hanger, in case any weights become loose and fall off the stack

#### Exam Tip

There is a lot of information to take in here! When writing about experiments, a good sequence is as follows:

• If you need to use an equation to calculate something, start off by giving it as this will give you some hints about what you need to mention later
• List the apparatus that you need
• State what measurements you need to make (your equation will give you some hints) and how you will measure them
• Finally, state that you will repeat each measurement several times and take averages ### Author: Jonathan

Jonathan graduated with a first-class Master's degree in Theoretical Physics from Imperial College London. He has worked in education for more than a decade as a Maths and Physics Teacher, Tutor, Head of Physics, and most recently, as Assistant Headteacher. He is now an Educational Consultant and works with us to design and improve our Physics resources.
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