Topic 9 - Forces and their Effects

• What is a force?

  A push or pull that acts on an object due to the interaction with another object
• What are the two categories that all forces can be split into?

  1. Contact forces (objects touching)

  2. Non-contact forces (objects separated)
• Give three examples of contact forces


  1. Friction

  2. Air resistance

  3. Tension
• Give three examples of non-contact forces

  1. Gravitational forces

  2. Electrostatic forces

  3. Magnetic forces
• Is force a vector or a scalar quantity? Why?

  ● Vector

  ● It has both a magnitude and an

  associated direction
• What is a scalar quantity?

  A quantity that has only magnitude and no direction
• What is a vector quantity?

  a quantity that has both magnitude and direction
• Give three examples of vector quantities

  1. Velocity

  2. Displacement

  3. Force
• Give three examples of scalar quantities

  ● Temperature

  ● Time

  ● Mass

  ● Speed

  ● Distance

  ● Energy
• How are vectors represented?

  With arrows - the length shows the magnitude and the direction of the arrow shows the direction of the vector.
• How can you calculate the resultant magnitude and direction of forces using a scale drawing?

  - draw the component forces as scaled arrows, joined tip-to-tail

  - draw a line connecting the two open ends

  - measure the length of this line and convert into the magnitude

  - measure the angle between the resultant line and the vertical/horizontal to find the direction.
• What is an alternative name for the turning effect of a force?

  moment
• State the equation used to calculate the moment of a force. Give appropriate units.


  Moment of force = Force x Distance Moment (Nm), Force (N), Distance (m)
• What distance measurement is used when calculating a moment?

  The perpendicular distance from the pivot to the line of action of the force.
• If an object is in equilibrium, what can be said about the moments acting on the object?

  The clockwise moments are equal to the anticlockwise moments.
• How do levers make use of moments?

  They increase the perpendicular distance of the force from the pivot, so decrease the force needed to produce the same moment.
• How are levers used to decrease the force required to lift something?

  Levers use a pivot point and the concept of moments to reduce the force. The further you are away from the pivot point, the less force you need to lift the object up.
• How does lubricating levers/gears improve efficiency?

  There is less resistance; less energy is wasted/dissipated (as heat) overcoming frictional forces