P5

• Definition of force

  A force is a pull that acts on an object due to its interaction with another object. Force is measured in newtons
• Force measurement example


  • When a hand pushes a box, it exerts a force like five newtons
• Forces

  Classified as vector quantities because they have both magnitude and direction
• Types of forces

  • Contact forces
  • Non-contact forces
• Contact forces

  Require the two objects to be physically touching
• Non-contact forces

  Do not require the two objects to be physically touching
• Contact forces

  • Friction, air resistance, tension, normal contact force
• Non-contact forces

  • Gravitational force, magnetic force, electrostatic force
• Gravitational force

  Force of attraction between any two objects that have mass
• Magnetic force

  Can be attractive or repulsive depending on the poles of the magnets
• Electrostatic force

  Between charged objects and can be attractive or repulsive
• Strength of non-contact forces

  Decreases as the objects get further apart
• Difference between scalar and vector quantities

  1. Scalars are physical quantities that only have a magnitude but no direction

  2. Vectors have both a magnitude and a direction
• Scalars


  Physical quantities that only have a magnitude but no direction
• Vectors

  Physical quantities that have both a magnitude and a direction
• Scalars


  • Distance
  • Mass
  • Temperature
  • Time
• Vectors


  • Velocity
  • Displacement
  • Acceleration
  • Force
  • Momentum
• Distance doesn't give any idea of direction, making it a scalar quantity
• Displacement gives both magnitude and direction, making it a vector quantity
• Representation of vectors

  • Arrows with length indicating magnitude and direction
• • Representation of a vector: 4 kilometers north is represented by an arrow pointing upwards
  • Representation of a vector: 2 kilometers west is represented by an arrow pointing left and half the size of the 4 kilometer north arrow
• Negative vectors can be represented e.g. -2 kilometers east
• Arrows are used to represent vectors with length indicating magnitude and direction
• What will be the resultant force acting upon this object?

  10N to the right

  
• what's the resultant force

  25N to the left

  
• what's the resultant force

  0N nor resultant force

  
• The train is travelling at a constant velocity because the forces acting on it are in equilibrium. 

  Therefore, the missing force must have a magnitude of 800 newtons to the right.

  
• Free body diagrams use arrows to show all of the forces acting on an object. 

  The length of each arrow indicates the magnitude of that force.

  The direction of each arrow indicates the direction of the force.
• what represents the resultant force: A

  
• Using scale drawings to find the resultant force on an object

  Represent the forces as arrows on a grid, place the vectors tip to tail, draw a line from the starting point to the end point to find the resultant force, measure the length to determine the magnitude, measure the angle to determine the direction
• Example of finding the resultant force

  • Man on a bike peddling with 4 newtons northwards and a strong breeze blowing him eastwards with 3 newtons, resulting in a 5 newton force at 37 degrees from north
• If forces balance, the object will be at equilibrium
• Finding the overall force when forces balance

  Arrange all arrows tip to tail, if they form a perfect triangle, there is zero resultant force
• Resolving vectors

  Splitting a vector into its horizontal and vertical components, representing the force with arrows on a scale drawing, measuring the horizontal and vertical components to determine their magnitudes
• Example of resolving a vector

  • Exerting a 50 newton force on a toy car up a ramp, resolving into a 40 newton force to the right and a 30 newton force upwards
• The term 'deformation' refers to a change in the shape of an object as a result of forces being applied to it. 

  If an object does return to its original shape after the forces have been removed, it is known as elastic deformation.

  On the other hand, if an object does not return to its original shape after the forces have been removed, it is known as inelastic deformation
• Extension is the increase in length of a spring when its stretched. Be aware that it can also refer to a decrease in length, if the spring is compressed. 
• An object's spring constant is a measure of how many Newtons of force it would require to stretch (or compress) the object by 1 metre. It has the units N/m
• Hooke's Law states that the extension of an object is directly proportional to the force applied.

  It can be described by the formula:

  F=ke

  Where 'F' is the force applied to the spring, ''k is the spring constant, and 'e' is the extension.
• The elastic limit is the point at which an object being stretched stops deforming elastically, and starts deforming inelastically.