(4.1) Force, Energy and Momentum

• Examples of scalars

  s peed, m ass, t ime, e nergy, p ower
• Examples of vectors

  d isplacement, v elocity, a cceleration, f orce, w eight
• Three conditions for a body to remain in equilibrium

  1. resultant force acting on body is 0

  2. resultant moment about any point is 0

  3. object could be stationary OR travelling at constant velocity
• Definition of the moment of a force about a point

  force multiplied by the perpendicular distance from the point to the line of action of the force.
• Units of moment

  Nm (Newton-meter)
• Principle of Moments

  in equilibrium, the sum of the clockwise moments about a point equals the sum of the anticlockwise moments.
• Definition of a couple

  A pair of forces, which are e qual, o pposite and c oplanar
• Definition of the moment of a couple

  A force multiplied by the perpendicular distance between the lines of actions of the two forces.
• Definition of centre of gravity

  Point in a body through which weight appears to act
• What is the gradient of a displacement-time graph?

  Velocity
• What is the gradient of a velocity-time graph?

  Acceleration
• What is the area under a velocity-time graph?

  Displacement
• What is the area under an acceleration-time graph?

  Velocity
• At constant speed, what is the net force?

  Zero
• If net force is zero, what is the equation balancing the forces?

  Driving Force = Resistive force (Friction and/or air resistance) + Parallel component of gravity
• Work done against gravity equation:

  GPE (mgh)
• Work done against friction equation:

  Frictional Force * Distance
• Frictional Force Equation:

  Perpendicular component of weight * coefficient
• Net work done equation:

  Work done by force - work done against gravity, friction and air resistance
• Net work done is also equal to:

  Change in kinetic energy (1/2mv^2)
• What equation does Net Force relate to?

  Newton's Second Law (F=ma)
• What equipment is needed for a mass-spring system experiment?

  Spring, masses, stand, clamp, ruler, stopwatch
• What is the first step in the mass-spring system method?

  Set up the apparatus without masses
• When should the stopwatch be started in the mass-spring system experiment?

  When the mass passes the fiducial marker
• How is the time period T calculated in the mass-spring system experiment?

  Divide T₁₀ by 10
• What is the maximum total hanging mass used in the mass-spring system experiment?

  500g
• Why is it important to repeat the mass-spring experiment multiple times?

  To find and record the mean T for each m
• What is the relationship between T² and m in the mass-spring system?

  • Plot T² against m
  • Gradient = $\frac{4\pi^2}{k}$
• What safety precaution is mentioned for the mass-spring system experiment?

  Do not attach too heavy masses
• What should be done if the spring moves horizontally during oscillation?

  Stop and restart the oscillation vertically
• How can timing more oscillations improve the experiment's accuracy?

  It reduces the percentage uncertainty in T
• What is the purpose of the fiducial marker in the mass-spring experiment?

  To mark the equilibrium position for timing
• What equipment is needed for a simple pendulum experiment?

  Pendulum bob, string, stand, clamp, ruler, stopwatch
• What is the length L set for the pendulum in the experiment?

  1.500m
• What should be done after pulling the pendulum to the side?

  Release it for small amplitude oscillations
• How is the time period T calculated for the pendulum?

  Divide T₁₀ by 10
• What is the minimum length L for the pendulum in the experiment?

  0.500m
• What is the relationship between T² and L in the simple pendulum experiment?

  • Plot T² against L
  • Gradient = $\frac{4\pi^2}{g}$
• What notable risks are associated with the simple pendulum experiment?

  No notable risks
• What is recommended for measuring the length of the pendulum bob?

  Use a small bob for easier measurement