Newton's Laws of Motion

• What does Newton's First Law of Motion state?

  Objects will remain at rest, or move with a constant velocity unless acted on by a resultant force

  
• What happens if the resultant force acting on an object is zero?

  The object will remain stationary if it was stationary before or continue to move at the same velocity if it was moving
• How does an object behave if it was moving before and the resultant force is zero?

  It will move at the same speed and in the same direction as before
• What is required for an object to move with a constant velocity?

  • The forces acting on the object must be balanced
  • The resultant force must be zero
• Is the Moon's orbit around the Earth an example of Newton's First Law of Motion? Explain.

  No, because the Moon is not moving with a constant velocity as it continually changes direction

  
• What does Newton's Second Law of Motion state?

  The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the object's mass
• What happens to an object's acceleration if the resultant force increases?

  The larger the resultant force, the larger the acceleration
• How does mass affect acceleration for a given force?

  The greater the object's mass, the smaller the acceleration experienced
• What is the equation for Newton's Second Law?

  F = ma
• In the equation F = ma, what does each variable represent?

  F = resultant force in Newtons (N), m = mass in kilograms (kg), a = acceleration in metres per second squared (m/s²)

  
• If a car has a mass of 900 kg and accelerates at $9 \text{ m/s}^2$, what is the force required?


  $F =$$900 \times 9 =$$8100 \text{ N}$
• How does the mass of an object affect its acceleration when the same force is applied?

  A larger mass will experience a smaller acceleration
• What is the estimated acceleration of a car that comes to a halt from $20 \text{ m/s}$ in $0.1 \text{ s}$?


  $a \approx -200 \text{ m/s}^2$
• If a passenger has a mass of approximately $70 \text{ kg}$ and experiences an acceleration of $-200 \text{ m/s}^2$, what is the force on the passenger?


  $F \approx 70 \times -200 =$$-14000 \text{ N}$
• What is the aim of the experiment investigating the effect of varying force on acceleration?

  • To investigate the effect of varying force on the acceleration of an object of constant mass
  • Independent variable: force (F)
  • Dependent variable: acceleration (a)
  • Control variable: mass (m)
• What is the aim of the experiment investigating the effect of varying mass on acceleration?

  • To investigate the effect of varying mass on the acceleration of an object produced by a constant force
  • Independent variable: mass (m)
  • Dependent variable: acceleration (a)
  • Control variable: force (F)
• What equipment is used in the experiments investigating force and acceleration?

  • Metre ruler (resolution = 1 mm)
  • Stopwatch (resolution = 0.01 s)

  
• What is the method for investigating the effect of force on acceleration?

  1. Measure intervals on the bench (e.g., every 0.2 m)
  2. Attach a bench pulley and tie string to a toy car
  3. Release the car and start the stopwatch simultaneously
  4. Record results and repeat for decreasing weights

  
• What is the method for investigating the effect of mass on acceleration?

  1. Measure intervals on the bench (e.g., every 0.2 m)
  2. Attach a bench pulley and put a 200 g mass on the car
  3. Tie string to the car and release it
  4. Record results for different masses

  
• What is the aim of Experiment 2?

  The aim is to investigate the effect of varying mass on the acceleration of an object produced by a constant force.
• What is the independent variable in the experiment?

  The independent variable is mass, m.
• What is the dependent variable in the experiment?

  The dependent variable is acceleration, a.

  
• What are the control variables in the experiment?

  • Force, F
• How do you measure intervals on the bench for the experiment?

  Use a metre ruler to measure out intervals, e.g., every 0.2 m for a total distance of 1 m.
• What should you do after measuring the intervals on the bench?

  Draw straight lines with pencil or chalk across the table at these intervals.
• What is the first step in the method of the experiment?

  Attach the bench pulley to the end of the bench.
• What mass should be put on the car for the experiment?

  A 200 g mass should be put on the car.
• How should the string be positioned in relation to the toy car or trolley?

  The string should be horizontal and in line with the toy car or trolley.
• What should you do to start the timing of the experiment?

  Release the car at the same time as starting the stopwatch.
• Why is it important to record results in a table?

  To determine the average speed of the trolley between intervals.

  
• How do you calculate the average speed per interval?

  Use the distance between each interval (0.2 m) and the average time taken to travel that distance.
• What equation is used to calculate acceleration between the first and last intervals?

  Acceleration is calculated using the change in speed over time.

  
• What is a systematic error in the experiment?

  Ensuring any weights removed from the weight hanger are transferred to the toy car or trolley.
• What is a random error in the experiment?

  A main cause of error is the measurements of time.
• How can you minimize random errors in timing?

  Take repeat readings when timing intervals and calculate an average.
• What should you avoid doing when starting the toy car?

  Do not give it a 'push'.
• What safety consideration should be taken into account?

  Don't stand directly beneath the weight hanger.
• What does Newton's third law of motion state?

  Whenever two bodies interact, the forces they exert on each other are equal and opposite.

  
• What do force pairs in Newton's third law represent?

  All forces arise in pairs; if object A exerts a force on object B, then object B exerts an equal and opposite force on object A.

  
• How does Newton's third law explain walking?

  The foot pushes the ground backwards, and the ground pushes the foot forwards.