P10 Force and Motion

• What must act on an object for its velocity to change?

  A resultant force
• In which direction is acceleration relative to the resultant force?

  Same direction as the resultant force
• What causes the force of gravity close to Earth?

  The planet's gravitational field strength
• What is weight defined as?

  The force acting on an object due to gravity
• Where can weight be considered to act on an object?

  • At the object's centre of mass
• How can weight be measured?

  Using a calibrated spring-balance
• What is the formula for weight?

  Weight (N) = mass (kg) × gravitational field strength (N/kg)
• What does the equation W = mg represent?

  Weight equals mass times gravitational strength
• How are weight and mass related?

  They are directly proportional to each other
• What happens to weight if the mass of an object doubles?

  Its weight also doubles
• What forces act on an object falling through a fluid?

  • Weight due to gravity
  • Drag force
• What happens to the weight of an object as it falls through a fluid?

  The weight remains constant
• How does the drag force change as an object speeds up in a fluid?

  The drag force gets bigger
• What happens to the resultant force as the drag force increases?

  The resultant force gets smaller
• What happens to the acceleration of an object as it falls through a fluid?

  The acceleration decreases
• What is terminal velocity?

  Constant velocity when drag equals weight
• What is the acceleration due to gravity when only acted on by gravity?

  9.8 m/s²
• What occurs as an object begins to fall?

  1. No drag initially
  2. Weight causes acceleration at 9.8 m/s²
• What happens as the velocity of a falling object increases?

  1. Frictional drag force increases
  2. Resultant force decreases
  3. Acceleration decreases
• What occurs when a falling object reaches terminal velocity?

  • Frictional drag balances weight
  • No resultant force, no acceleration
• What does Newton's Second Law state about acceleration?

  Acceleration is proportional to resultant force
• How is acceleration related to mass according to Newton's Second Law?

  Acceleration is inversely proportional to mass
• What is the equation linking resultant force, mass, and acceleration?

  Resultant force (N) = mass (kg) × acceleration (m/s²)
• What happens when a skydiver jumps out of a plane?

  He accelerates due to gravity.
• How can inertial mass be calculated?

  Inertial mass (kg) = force (N) / acceleration (m/s²)
• What is momentum?

  A property of all moving objects
• Why does a skydiver continue to accelerate after jumping?

  Air resistance is less than his weight.
• What is terminal speed in skydiving?

  When air resistance equals weight.
• What factors does momentum depend on?

  Mass and velocity of an object
• What happens when the parachute opens?

  Air resistance increases, slowing the parachutist.
• What occurs as the parachutist slows down after the parachute opens?

  Air resistance decreases until balanced with weight.
• What is the equation for momentum?

  Momentum (kg m/s) = mass (kg) × velocity (m/s)
• How does the terminal speed after opening the parachute compare to before?

  It is a much slower terminal speed.
• What does the Law of Conservation of Momentum state?

  • Total momentum before an event equals after
  • Applies to collisions and explosions
• What factors affect thinking distance and braking distance?

  • Speed of travel
  • Effects of drugs
  • Alcohol
  • Tiredness
  • Road conditions
  • Distractions
  • Mass of the car
  • Conditions of tyres
  • Conditions of brakes

  
• What safety feature in cars reduces injuries in a crash?

  Air bags
• How can the law of conservation of momentum be expressed for two colliding objects?

  m1u1 + m2u2 = m1v1 + m2v2
• How do air bags work to reduce injury?

  They increase the time of impact.
• What do the symbols m1 and m2 represent in the momentum equation?

  Mass of object 1 and object 2
• What is the relationship between force, mass, change in velocity, and time of impact?

  F = m $\Delta v$ / $\Delta t$