Investigating the Relationship Between Force, Mass, and Acceleration Summary

Core Practical: Investigating the Relationship Between Force, Mass, and Acceleration

Overview

  • P2.19: Core Practical focusing on the relationship between force, mass, and acceleration.
  • Experiment involves varying masses added to trolleys.
  • Students should know how to perform this practical using light gates.

Student Requirements

  1. Context and Aim:

    • One or two sentences setting out the context and aim, including the three variables (force, mass, acceleration).
    • Example: "Newton’s second law says that mass and force are directly proportional. We will complete an experiment to test this by varying the mass whilst keeping the force constant."

  2. Method:

    • A list of instructions detailing the experimental procedure.
    • A list of all key equipment used (can be within the method or separate).

  3. Risk Assessment:

    • At least two identified hazards associated with the practical.

  4. Results Table:

    • A results table with clear headings and units.

  5. Calculating Acceleration:

    • Explanation of how to find acceleration, including the relevant equation.

  6. Scatter Graph:

    • Scatter graph of mass against acceleration with a line of best fit.
    • Axes labelled with units.

  7. Graph Questions:

    • Answers to questions about the graph (relationship between variables, etc.).

  8. Evaluation Questions:

    • Answers to evaluation questions (quality of data, comparison with other results, etc.).

  9. Percentage Uncertainty Calculation:

    • Calculation of percentage uncertainty for one result.
    • Statement about the accuracy of the result compared to the calculation.

  10. Home Learning:

    • Related to understanding of light gates.

Key Concepts and Objectives

  • Keywords: mass, weight, gravitational field strength, force meter, force, acceleration.
  • Objective: Identify hazards and safely carry out a practical.

Background: Newton's Second Law

  • Equation: F=m×aF = m \times a where:
    • FF = Resultant Force (N)
    • mm = Mass (kg)
    • aa = Acceleration (m/s²)
  • Newton's Second Law states that the acceleration of an object depends on the force applied and the object’s mass.
  • The experiment utilizes the weight of masses to accelerate a trolley.

Calculating Acceleration

  • Acceleration calculation formula:
    • a=v−uta = \frac{v - u}{t}
    • aa = acceleration
    • vv = final velocity
    • uu = initial velocity
    • tt = time
  • Speed calculation:
    • speed=distancetimespeed = \frac{distance}{time}

Light Gates

  • Light gates emit a thin beam of light.
  • When an object breaks the beam, a digital readout measures the duration of the break.

Procedure

  • Aim: To investigate how changing the mass of the trolley affects its acceleration when the force is constant.
  • Method:
    1. Set up the equipment.
    2. Weigh the trolley to find its mass.
    3. Use a Newton meter to measure the force from the hanging masses.
    4. Adjust the ramp until the trolley starts to roll (to account for friction).
    5. Hold the trolley and attach the string with hanging masses.
    6. Release the trolley.
    7. Measure the time for the trolley to pass through light gates at the top and bottom of the ramp.
    8. Add mass to the trolley and repeat the experiment.
  • Variables:
    • Independent Variable: Mass of the trolley + weights.
    • Dependent Variable: Acceleration of the trolley.
    • Control Variable: Resultant force acting on the trolley.
  • Equipment:
    • Ramp
    • Masses and hanger
    • Trolley
    • Newton meter
    • Light gates
    • Ruler
    • String
  • Hazards:
    • Mass falling onto someone.
    • Trolley and masses falling off the end of the ramp.
  • Prevention:
    • Stand to the side of the experiment.

Results Table

Mass added to trolley (kg)Total mass of trolley (kg)Initial time (s)Initial velocity (m/s)Final time (s)Final Velocity (m/s)Acceleration (m/s²)Length of card (mm)Mass of Trolley (kg)Force from hanging mass (N)
0.1
0.2
0.3
0.4
0.5

Alternative Results Table

Mass addedTime 1 (s)Time 2 (s)Time 3 (s)Mean Time (s)Mean Speed (m/s)Acceleration (m/s²)
0
1
2
3
4
5

Graphing

  • X-axis: Total mass of trolley and masses (kg).
  • Y-axis: Acceleration = change in speed ÷ time (m/s²).
  • Plot a scatter graph of mass against acceleration.
  • Draw a line of best fit.
  • Calculate the gradient of the line.

Graph Questions

  1. Describe the relationship between acceleration and mass shown on your graph.
  2. Is this what you predicted?
  3. What value (that you controlled in the experiment) is given by the gradient of the line?

Evaluation Questions

  1. How close are your points to the line of best fit?
  2. What does this tell you about the quality of your data?
  3. How do your results compare with other groups? (give one similarity and one difference.)
  4. How certain are you that your results are correct?
  5. How similar was your value of force measured to the value of the gradient?
  6. Describe factors that may have affected our results.

Analysis: Percentage Uncertainty

  • Calculate the percentage uncertainty in your value for force measured from the gradient.
  • Formula:
    Percentage:Uncertainty=∣Gradient:value–Measured:Value∣Measured:value×100Percentage :Uncertainty = \frac{|Gradient : value – Measured : Value|}{Measured : value} \times 100

Summary

  • Testing Newton’s 2nd Law
  • Independent variable:
  • Dependent Variable:
  • Control Variable:
  • Method:
    1. Weight the trolley
    2. Time how long for the trolley to move
    3. Calculate acceleration
    4. Plot graph.
  • Conclusion: As the mass increased so did the acceleration.
  • Hazards: Be careful that the mass doesn’t hit your foot. Stand well back.

Calculations: Initial and Final Velocities, Acceleration

  • Initial Velocity:
    • Using the initial distance (e.g., 0.1m) and the time it took to cover that distance, calculate initial velocity.
    • Initial:velocity=0.1timeInitial : velocity = \frac{0.1}{time}
  • Final Velocity:
    • Using the final distance (e.g., 0.1m before the end) and the time it took to cover that distance, calculate final velocity.
    • Final:velocity=0.1timeFinal : velocity = \frac{0.1}{time}
  • Acceleration:
    • Using the time the trolley was accelerating, calculate the acceleration using the equation:
    • a=v−uta = \frac{v - u}{t}

Sample Exam Question

  • A student investigates how the average speed of the trolley varies with starting height. Describe how the student can determine the average speed of the trolley.
    *Answer
    *Additional Guidance
    *Mark
    *An answer that combines the
    allow
    following points of
    understanding to provide a
    logical description:
    measurement of time.
    between(or at) two
    positions using
    suitable timing
    equipment (1)
    stopwatch, light gates.
    measurement of
    minimum is 0.5 m
    suitable distance
    along the runway
    metal tape measure
    with metre rule (1)
    measurement of vertical
    average speed =
    distance/time

OR
height to starting position average speed = (speed at
B)/2
(1)
repeats AND averages
AND use of a correct
equation (1)
(4)
*How could you improve your answer?

Homework

  • Complete the exam questions on page 305 of the combined science textbook (through activelearn).
  • Due in next lesson, needs to be in front of you so we can self assess. HAND IN YOUR BOOKS