Forces

• What is a scalar quantity


  Have magnitude only
• What is a vector quantity

  Have magnitude and direction
• How are forces represented

  As a vector which means it has both magnitude and direction
• What can forces change

  • Shape
  • Speed
  • Velocity (to accelerate)
• Examples of vector quantities

  • Velocity
  • Displacement
  • Weight
  • Force
  • Acceleration
  • Momentum
• Examples of scalar quantities

  • Time
  • Distance
  • Energy
  • Speed
  • Power
• How are vector quantities represented

  By an arrow. The length of the arrow represents the magnitude, the direction of the arrow and the direction of the vector quantity
• What are contact forces

  Objects are physically touching
• What are non-contact forces

  The objects are physically separated
• Examples of contact forces

  • Friction
  • Tension
  • Normal contact force
  • Air resistance
• Examples of non-contact force

  • Electrostatic
  • Magnetic
  • Gravitational
• Why is air resistance a contact force

  Its due to its collision of an object and air particles.
• What is weight

  The force that acts on an object due to its gravity and object mass
• What does the weight of an object depend on

  The gravitational field strength at the point where the object is and mass
• Equation for weight

  weight = mass x gravity
• What is meant by an objects centre of mass

  The single point where an objects weight can be considered to act through
• What equipment can be used to measure weight

  • Newton meter
  • Calibrated spring balance
• What does it mean if a force is said to do 'work' on an object


  The force causes an object to be displaced through a distance
• Equation for work done linking force


  Work done = force x distance

  W = F x S
• What is 1 joule of work done


  When a force of 1 newton causes a displacement of 1 metre
• How many newton metres are equal to 1 joule of energy


  1Nm = 1 joule of energy
• What occurs when work is done against frictional forces

  • A rise in temperature of the object
  • Kinetic energy is transferred to heat
• Explain why to change the shape of an object more than one force has to be applied - stationary objects only


  If there was just one force acting on the object, then it would accelerate in the direction of that force.
• What is elastic deformation


  If an object does return to its original shape after the forces have been removed
• What is inelastic deformation


  If an object does not return to its original shape after the forces have been removed
• Explain the relationship between the force applied and the extension of an elastic object


  Extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded
• Equation linking force and extension


  force = spring constant x extension

  F = K x E

  N = N/M x METRES
• How to work out extension


  extension = changed length - original
• What can extension be replaced with in the equation for spring force


  Compression
• Describe the difference between a linear and non-linear relationship between force and extension

  • For a linear relationship between force and extension, the gradient of the force (extension graph) is equal to the spring constant as force and extension are directly proportional
  • while for a non-linear relationship between force and extension, the gradient of the force (extension graph) is not equal to the spring constant
  • as force and extension aren't directly proportional
  • the extension increases more for each unit increase in force
• What is limit of proportionality

  maximum amount of force that can be applied before the force is no longer proportional to the extension.
• What is the difference between linear and non-linear relationship for limit of proportionality


  Up until the point, the relationship between force and extension is linear and directly proportional. After this the graph curves, because force is no longer proportional to extension.
• RP 18: Forces and extension

  1. Secure clamp stand to bench
  2. Use bosses to attach two clamps to the clamp stand.
  3. Attach the spring to the top clamp, and a ruler to the bottom clamp.
  4. Adjust the ruler so its vertical, and with its zero level with the top of the spring.
  5. Measure and record the unloaded length of the spring and take a reading of the ruler
  6. Record this in a table
  7. Add a 100 g slotted mass to carrier. Measure and record the length of the spring.
  8. Add further weights. Measure and record the length of the spring each time.
  9. Calculate extension for each weight and record it on table
• What is distance


  • how far an object moves
  • its a scalar quantity as it doesn't involve direction
• What is displacement


  Vector quantity of how far an object moved from its original position with a direction
• What is speed


  • It does not involve direction
  • Scalar quantity
• Equation for speed


  speed = distance / time
• State the typical value for the speed for sound

  330m/s
• State the typical value for the speed for walking

  1.5m/s
• State the typical value for the speed for running

  3m/s