forces in action

• What does Newton's second law define?

  The relationship between net force, mass, and acceleration
• What is the equation for Newton's second law?

  Net force = mass × acceleration
• What does 'net force' refer to?

  The total force acting on an object
• If one newton acts downwards and no other forces act, what is the net force?

  One newton
• What happens to the net force when equal and opposite forces act on an object?

  The net force becomes zero
• If a box has one newton down and two newtons up, what is the net force?

  One newton upwards
• What unit is used to measure force?

  Newton
• How is a newton defined in physics?

  Force to accelerate 1 kg by 1 m/s²
• What is the formula for weight?

  Weight = mass × gravity
• What is the value of g on Earth?

  9.81 m/s²
• What direction does weight always act?

  Vertically downwards
• What is the normal force?

  An upward force opposing weight
• What principle explains the normal force?

  Electrostatic force and repulsion of electrons
• What is upthrust?

  A force acting upwards on submerged objects
• What does friction do?

  Opposes the motion of an object
• What is a free body diagram?

  A diagram showing all forces acting on an object
• How do you represent forces in a free body diagram?

  With arrows proportional to their magnitude
• What does a net force of zero indicate about an object's motion?

  The object is at constant velocity or at rest
• If a helicopter lifts a 100 kg mass at constant velocity, what is the tension in the cable?

  980 newtons
• What does constant velocity imply about net force?

  No resultant force is acting on the object
• How do you calculate tension when an object accelerates?

  Tension = weight + mass × acceleration
• What is drag force?

  A force opposing the motion of an object through a fluid
• What happens to drag force as an object's speed increases?

  Drag force increases with speed
• What is terminal velocity?

  The constant speed when drag force equals weight
• How can you investigate the motion of a ball bearing in a fluid?

  Drop it in a tube and measure time intervals
• What does a graph of speed against time show for a falling object?

  A curve showing decreasing acceleration to terminal velocity
• What happens to the forces acting on a skydiver at terminal velocity?

  Weight equals drag force
• How do you split the weight of an object on an inclined plane?

  Into components parallel and perpendicular to the plane
• What is the relationship between the angle of incline and the components of weight?


  They depend on the angle theta
• What is the parallel component of weight on an incline?

  mg sine theta
• What is the perpendicular component of weight on an incline?

  mg cos theta
• What does the center of gravity represent?

  Point where weight acts
• How can the center of mass be determined practically?

  Using a plumb line and intersection of lines
• What is the definition of a moment of force?

  Product of force and distance from pivot
• What happens when a force is applied to a seesaw?

  It creates a turning effect
• How is a moment calculated when the force is not perpendicular?

  Using the perpendicular distance to the line of action
• What is the moment of a 5 N force at a distance of 0.1 m?

  0.5 N·m
• What is the principle of moments?

  Sum of anti-clockwise moments equals clockwise moments
• What defines a force couple?

  Two equal and opposite forces
• How is torque defined?

  Net moment caused by forces