topic p5- forces

• vectors

  • forces are a vector quantity
  • this means they have a magnitude and direction
• examples of vectors include

  • displacement
  • velocity
  • acceleration
• scalars

  • some physical quantities are scalar
  • this means they only have a magnitude
• examples of scalars include

  • distance
  • speed
  • time
• forces can be

  contact of non-contact
• contact forces

  • friction
  • air-resistance
  • normal contact force
• non-contact forces

  • magnetic
  • gravitational
  • electrostatic
• weight

  
• w = m g

  weight (N) = mass (kg) x gravity (N/kg)
• acceleration

  
• acceleration (m/s^2) =

  final velocity (m/s) - initial velocity (m/s) / time (seconds)
• work done

  
• w = f s

  work done (Nm) = force (N) x displacement (m)
• momentum

  
• p = m v

  momentum (kg m/s) = mass (kg) x velocity (m/s)
• resultant forces

  free body diagrams are used to show all forces acting on an object

  
• resultant force calculation

  • the forces going up and down are equal (500 N each), meaning the car is not moving vertically
  • the car has a driving force of 1000 N and friction force of 100 N
  • by subtraction, the car has a 900 N resultant force going forwards (to the right)
• elasticity- force vs extension

  • force is proportional to extension up to a certain point
  • this point is known as the limit of proportionality
  • before this point, the object being deformed is elastic, meaning it will return to its original shape
  • after this point, the object being deformed becomes inelastic or plastic
  • this means it will no longer return to its original shape
• elasticity

  A)

  
• force = spring constant x extension

  f = k . x

  (N) = (N/m) (m)
• be careful when explaining different sections of these graphs

  
• distance- time graphs

  1. constant speed
  2. stopped/ at rest
  3. accelerating
  4. decelerating

  • the gradient of a distance time graph is the speed at the respective time
• velocity-time graphs

  1. constant acceleration
  2. constant speed
  3. increasing acceleration
  4. decreasing acceleration

  • the area under a velocity time graph is the distance (travelled)
  • the gradient of a velocity time graph is the acceleration at the respective time
• how many newtons laws are there

  3
• newtons first law

  an object will stay in motion unless acted upon by an unbalanced external force
• newtons first law

  • if a ball is at rest, it will remain at rest unless pushed
  • if a car is moving, it will continue unless the brakes are applied or friction slows it down

  
• newtons second law

  the law of inertia:

  force = mass x acceleration
• newtons second law

  • force is proportional to acceleration
  • if an object has 10kg of mass, and acceleration at 10 m/s^2, then its force is 100N

  
• newtons third law

  for every force, there is an equal and opposite force
• newtons third law

  • a normal contact force is typically labelled as this 'opposite' force
  • if this force didn't exist, objects would go straight through each other