forces

• Scalar quantity


  Quantity that has magnitude (size) only, and no direction
• Vector quantity


  Quantity that has both magnitude (size) and direction
• Distance (scalar)


  Gives no idea of direction
• Displacement (vector)


  Gives both magnitude and direction
• Representing vectors


  • Using an arrow, where the length represents the magnitude and the direction represents the direction of the vector
• Force


  A push or pull that acts on an object due to the interaction with another object
• Types of forces


  • Contact forces
  • Non-contact forces
• Contact forces


  Forces where the two objects are physically touching
• Contact forces


  • Tension in a rope
  • Friction (e.g. between airplane and water)
  • Air resistance (e.g. on a skydiver)
  • Normal contact force (e.g. between a lump and a table)
• Non-contact forces


  Forces where the two objects are physically separated
• Non-contact forces


  • Gravitational force (e.g. between Earth and International Space Station)
  • Electrostatic force (e.g. between charged objects)
  • Magnetic force (e.g. in a magnetic field)
• Weight


  The force acting on an object due to gravity
• Calculating weight


  Mass in kilograms x Gravitational field strength in Newtons per kilogram
• The equation for weight is not given in the exam, but the gravitational field strength will be provided
• Mass of an object


  Weight of the object is directly proportional
• Gravitational field strength


  A measure of the force of gravity in a particular location
• Gravitational field strength


  Depends on the location
• Center of mass


  The point at which the weight of an object can be considered to act
• Resultant force


  A single force that has the same effect as all of the original forces acting together
• Calculating resultant force


  Subtract the smaller force from the larger force
• Calculating resultant force


  • Example 1: Man pushing box, force of 20N right, friction force of 10N left, resultant force of 10N right
  • Example 2: Car, driving force of 10,000N left, friction force of 4,000N right, air resistance of 5,000N right, resultant force of 1,000N left
• Balanced forces


  • Example: Skydiver, weight of 800N down, air resistance of 800N up, resultant force is 0
• Free body diagram


  • Object shown as a point, forces drawn as arrows starting from the point, length of arrow shows size of force, direction of arrow shows direction of force
• Free body diagram


  • Example: Aeroplane, weight acting down, lift acting up, thrust acting forward, drag acting backward
• Resultant force is the single force that has the same effect as all the original forces acting together
• To calculate resultant force, subtract the smaller force from the larger force
• When forces are balanced, the resultant force is 0
• Free body diagrams show the object as a point and the forces as arrows starting from that point
• Resultant force

  The RESULTANT FORCE is the OVERALL FORCE resulting from the combination of all forces acting on an object. 

  To find the RESULTANT FORCE when multiple forces act along the same line:

  • ADD the forces moving in the SAME direction
  • SUBTRACT those in the OPPOSITE direction.
• Forces and Elasticity

   

  • When we apply more than one FORCE to a stationary object, it can cause DEFORMATION.
  • Deformation is when the object CHANGES SHAPE.
  • The DIRECTION the forces act in, and the POSITION they act from, determine the way the object will deform:
• 1. ELASTIC deformation

  This is when the object RETURNS TO ITS ORIGINAL SHAPE AND LENGTH after the forces have been removed.
• 2. INELASTIC deformation

  This is when the object DOESN’T return to its original shape and length after the forces have been removed.
• Hooke's Law

  The EXTENSION is the DIFFERENCE between the length of STRETCHED SPRING and the ORIGINAL LENGTH of the unstretched spring:

  he extension of an elastic object like a spring is DIRECTLY PROPORTIONAL to the force applied, given the LIMIT OF PROPORTIONALITY is not exceeded.
• ELASTIC LIMIT

  Eventually, if you add enough force to a spring, it will deform INELASTICALLY and will NOT return to its original shape and length. The point at which this happens is known as the ELASTIC LIMIT.
• ELASTIC POTENTIAL ENERGY

  The WORK DONE in stretching (or compressing) an elastic object is stored as ELASTIC POTENTIAL ENERGY within the object.

  During ELASTIC DEFORMATION: The WORK DONE is EQUAL to the ELASTIC POTENTIAL ENERGY stored in the object

  During INELASTIC DEFORMATION: Some of the WORK DONE is DISSIPATED as heat, meaning the object does NOT return to its original shape and size.
• Required Practical: Force and Extension

  1. Position the spring and attach a ruler beside it for measuring extension

  2. Record the spring's length without any added mass, which is its original length

  3. Place a 100 g mass hanger on the spring, which will extend due to the added weight

  4. Note the mass in kilograms and the extended length from the ruler in centimetres

  5. Continue to add 100 g increments to the mass hanger, each time recording the new total mass and the extension

  6. Remove the masses and repeat the process several times and find an average
• Extension


  The increase in length of the spring due to the added weight
• Analysis of Results


  To find the extension of the spring, subtract the original length from the final length for each measurement
• DISTANCE measures how far an object has travelled, regardless of its starting point or final position. It is a SCALAR quantity, meaning it only has magnitude and NO direction.DISPLACEMENT refers to how far an object is from its starting point and in what direction — it's a straight-line measurement from START to FINISH.

  Unlike distance, displacement is a VECTOR quantity because it considers both magnitude AND direction.
• SPEED is a measure of how fast an object is moving and is defined as the DISTANCE TRAVELLED in a given TIME.

  It is a SCALAR quantity, meaning it only considers magnitude and NOT direction.The SPEED OF SOUND in air, is roughly 330 m/s, and it can vary depending on what substance it travels through.

  VELOCITY is the speed of an object in a given DIRECTION, which makes it a VECTOR.