Force and motion

• What does the acceleration of an object depend on?

  The size of the resultant force
• How does mass affect acceleration?

  More mass results in less acceleration
• How do you calculate the resultant force from acceleration and mass?

  Use the formula F = ma
• What is inertia?

  The tendency to resist changes in motion
• What apparatus can be used to investigate force and acceleration?

  • Trolley
  • Newton meter
  • Motion sensor
  • Computer
• What happens to the acceleration of the trolley if the force is increased?

  The acceleration increases
• What happens to the acceleration of the trolley if its mass is increased?

  The acceleration decreases
• What should be done for safety when using the trolley?

  Protect your bench and feet
• What is the formula to calculate acceleration from a velocity-time graph?

  Acceleration = gradient of the line
• What does Newton's second law state about acceleration?

  It is proportional to resultant force
• How is the resultant force related to mass and acceleration?

  F = ma links them together
• What is the weight of an object?

  The force acting on it due to gravity
• How do you calculate weight?

  Weight = mass × gravitational field strength
• What is the weight of a person with a mass of 55 kg on Earth?

  Weight = 55 kg × 9.8 N/kg = 539 N
• What is terminal velocity?

  The constant speed reached when falling
• What happens to an object at terminal velocity?

  The weight equals the frictional force
• What affects the braking force needed to stop a vehicle?

  The mass and speed of the vehicle
• What is the equation for braking force?

  Braking force = mass × acceleration
• What are the two parts of stopping distance?

  Thinking distance and braking distance
• How is thinking distance calculated?

  Speed × reaction time
• What is the typical stopping distance at 31 m/s?

  96 m
• What factors affect stopping distances?

  • Speed of the vehicle
  • Mass of the vehicle
  • Reaction time of the driver
  • Road conditions
• What happens to the braking force as speed increases?

  It must increase for the same stopping distance
• How does mass affect the braking force needed?

  Greater mass requires greater braking force
• What is the relationship between deceleration and stopping distance?

  Greater deceleration means shorter stopping distance
• What is the effect of friction on a falling object?

  It opposes the motion of the object
• What happens when the upward force balances the downward force on a falling object?

  The object continues at constant speed
• What is the gravitational field strength on Earth?

  Approximately 9.8 N/kg
• How does gravitational field strength differ on the Moon?

  It is about 1/6th of Earth's
• How do you calculate the weight of a 100 kg object on the Moon?

  Weight = 100 kg × 1.6 N/kg = 160 N
• What is the effect of air resistance on a parachutist falling with a parachute?

  It reduces the acceleration until constant speed
• What happens to the forces acting on a parachutist when they reach constant speed?

  The upward force equals the downward force
• What is the relationship between drag force and weight at terminal velocity?

  Drag force equals weight at terminal velocity
• What is the typical acceleration of an object acted on only by gravity?

  About $10 \text{ m/s}^2$
• What is the significance of the resultant force being zero?

  The object moves at constant velocity
• How does the braking distance change with speed?

  It increases with higher speeds
• What is the effect of a driver's reaction time on stopping distance?

  Longer reaction time increases stopping distance
• What is the formula for calculating stopping distance?

  Stopping distance = thinking distance + braking distance
• What happens to the braking force if the mass of the vehicle increases?

  The braking force needed increases
• How does the relationship between force and acceleration change with mass?

  More mass requires more force for same acceleration