Physics - Topic 9 - Forces and their Effects

• What is an example of interaction of objects at a distance without contact?

  Gravitational attraction
• How does gravitational attraction depend on mass?

  The larger mass gives greater attraction
• What is the effect of a larger charge in electrostatic interactions?

  A larger charge gives greater force
• What happens when like charges interact?

  Like charges repel each other
• What is the behavior of opposite charges in electrostatic interactions?

  Opposite charges attract each other
• What is the effect of a stronger magnet in magnetic interactions?

  A stronger magnet gives a stronger field
• How do like poles behave in magnetic interactions?

  Like poles repel each other
• What is the behavior of opposite poles in magnetic interactions?

  Opposite poles attract each other
• What is the normal contact force?

  The force is perpendicular to the plane of contact
• What causes friction between surfaces?

  Rough surfaces cause friction when moved
• What defines a vector?

  A vector has size and direction
• Give an example of a vector.

  A force of 10N directed downwards
• What is a scalar?

  A scalar has just size
• Give an example of a scalar.

  Mass
• What do free body diagrams represent?

  • They show the direction of forces present in a situation
  • They help visualize the net force acting on an object
• What does the reaction force do in contact interactions?

  The reaction force acts at the normal to the line of contact
• In which direction does friction act?

  Friction acts in the opposite direction to movement
• How does weight act on an object?

  Weight always acts downwards
• What does the length of each arrow in a scale drawing represent?

  The length represents its size in relation to other forces
• What happens when arrows in a scale drawing are equal in length but opposite in direction?

  The forces cancel out, and the object is in equilibrium
• What does it mean for an object to be in equilibrium?

  It travels at a constant velocity
• What happens to the resultant force at point B in a diagram?

  The resultant force causes acceleration
• What happens to the resultant force at point C in a diagram?

  The resultant force is smaller, causing smaller acceleration
• What does an isolated solid system mean?

  No forces are present from a source outside the system
• What forces act on a skydiver?

  Air resistance and weight

  
• What happens to a skydiver as they fall?

  They accelerate, increasing their speed
• How does air resistance change as the skydiver accelerates?

  Air resistance increases
• What happens when weight and air resistance are equal for a skydiver?

  There is no resultant force and terminal velocity is reached
• What is terminal velocity?

  It is the constant speed reached when forces are balanced
• What happens to a vehicle's thrust as air resistance increases?

  Resultant force decreases
• What occurs when a vehicle reaches terminal velocity?

  Thrust is balanced by drag and friction
• What happens when more thrust is added to a vehicle at terminal velocity?

  It becomes the resultant force until drag increases to balance it again
• What is required for rotation to occur?

  An object must be attached to a pivot point
• What happens when a force is applied not towards the pivot?

  The object will not rotate and will just be held still
• What happens when a force is applied perpendicular to the object?

  It will move about the pivot in that direction
• How do you determine the direction of rotation when a force is applied not perpendicular?

  Find the perpendicular distance from the pivot to the line of force
• What is the formula for moment?

  Moment = Force × Distance perpendicular to the direction of the force
• What is the unit of moment?

  Newton metre (N m)
• How does pressing your foot down on a pedal create a moment?

  It causes a moment about the pivot, turning the pedal arms
• When does equilibrium occur in a system?

  When the sum of anticlockwise moments equals the sum of clockwise moments