Motions & Forces

• What is terminal velocity?

  Velocity remains constant with no acceleration
• What happens to an object when it first steps out of an airplane?

  It experiences a downward force due to weight
• What force pulls a person downwards when they jump from an airplane?

  Gravity
• What is the resultant force when a person first steps out of the plane?

  It is equal to the weight acting downwards
• What happens to the resultant force as a person starts falling?

  It causes the person to accelerate downwards
• What force opposes the weight of a falling person?

  Air resistance
• What is air resistance also known as?

  Drag
• What factors affect the size of air resistance on a falling object?

  Surface area and velocity of the object
• How does surface area affect air resistance?

  Larger surface area increases air resistance
• How does velocity affect air resistance?

  Higher velocity increases air resistance
• What happens to air resistance when a person accelerates downwards?

  Air resistance increases as velocity increases
• What does the resultant force equal when air resistance equals weight?

  Zero resultant force
• What occurs when the resultant force is zero?

  The object stops accelerating
• What is the term for the velocity at which an object stops accelerating?

  Terminal velocity
• What happens when a parachute is opened during a fall?

  Surface area increases, increasing air resistance
• What is the effect of increased air resistance after opening a parachute?

  Resultant force becomes upwards, slowing descent
• What happens to the new terminal velocity with a parachute compared to without?

  It is lower with the parachute
• What are the key points about falling objects and terminal velocity?

  • Weight is greater than air resistance initially
  • Resultant force causes downward acceleration
  • Air resistance increases with velocity
  • Terminal velocity occurs when forces balance
  • Opening a parachute increases air resistance
  • New terminal velocity is lower with parachute
• What happens to the resultant force when air resistance equals weight?

  Resultant force is zero
• What is the relationship between acceleration and resultant force?

  Zero resultant force means no acceleration
• What is the effect of air resistance on a falling object?

  It opposes the weight of the object
• What does Newton's first law state about the motion of an object?

  A resultant force is required to change the motion of an object
• What happens to a stationary object if the resultant force on it is zero?

  It will remain stationary
• What happens to a moving object if the resultant force on it is zero?

  It will continue moving at the same velocity
• What does Newton's second law state about a non-zero resultant force?

  It causes the object to accelerate
• If an object is stationary and a resultant force acts on it, what will happen?

  It will start moving in the direction of the force
• If an object is moving to the right and a resultant force acts to the right, what will happen?

  It will speed up
• If an object is moving to the left and a resultant force acts to the right, what will happen?

  It will slow down
• What happens if an object is moving to the left slowly and a resultant force acts to the right?

  It could stop moving entirely
• What is the definition of acceleration?

  Change in velocity divided by change in time
• Why is the moon considered to be accelerating even though its speed is constant?

  Because its direction is always changing
• What is the relationship between resultant force and acceleration according to Newton's second law?

  Resultant force is directly proportional to acceleration
• If the resultant force on an object is doubled, what happens to its acceleration?

  It also doubles
• What is the equation for Newton's second law?

  $F =$$ma$
• What is inertia?

  The tendency for an object's motion to remain unchanged
• What does an object's inertial mass measure?

  How difficult it is to change the object's velocity
• If an object has a large mass, what does this imply about its inertia?

  It will require a large force to change its velocity
• What are the five possible outcomes of acceleration on an object?

  1. Start moving if stationary
  2. Speed up if moving in the same direction
  3. Slow down if moving in the opposite direction
  4. Stop moving if slowed down enough
  5. Change direction without changing speed
• What is the relationship between force, mass, and acceleration?

  • Force is directly proportional to acceleration
  • Mass is inversely proportional to acceleration
  • $F =$$ma$
• How does circular motion demonstrate acceleration?

  • Speed remains constant
  • Direction is constantly changing
  • Velocity changes due to direction change
  • Acceleration occurs because velocity changes