Forces and motion

• Distance is a scalar quantity
• speed is a scalar quantity
• temperature is a scalar quantity
• energy is a scalar quantity
• time is a scalar quantity
• displacement is a vector quantity
• velocity is a vector quantity
• acceleration is a vector quantity
• force is a vector quantity
• weight is a vector quantity
• An object is in equilibrium when the net force acting on it is zero, resulting in no acceleration.
• Speed is the rate of change of distance travelled over a completed journey. Measured in meters per second (m/s)
• Displacement is the distance travelled in a particular direction. measured in meters (m)
• Velocity is the rate of change of displacement, measured in metres per second (m/s)
• Acceleration is the rate of change of velocity, measured in metres per second squared (m/s2).
• Label the displacement time graph.

  >

  A) Constant velocity

  B) stationary

  C) acceleration

  D) deacceleration

  
• The gradient of a displacement time graph is velocity
• Label the velocity time graph:

  .

  A) constant acceleration

  B) constant velocity

  C) non-uniform acceleration

  
• The gradient of a velocity time graph is acceleration.
• The area underneath a velocity time graph is equal to displacement
• Friction is a force that opposes the movement between surfaces in contact.
• Contact friction occurs between two surfaces
• Drag occurs between a solid object and a fluid
• Drag increases as the objects speed increases
• Drag is affected by the thickness of the fluid and the shape and size of the object
• Drag cannot cause an object to start moving or increase its speed
• Terminal velocity is achieved when an object's weight and drag force are equal and opposite which results in a constant speed
• A falling object:

  1. Accelerates from standstill due to a constant driving force
  2. As the speed increases, the drag force increases, decreasing acceleration
  3. The driving force and drag force become equal leading to a constant speed, its terminal velocity
• To determine terminal velocity:

  1. Fill a clear vertical tube with a viscous liquid
  2. Drop a ball bearing into the tube and use a stopwatch to time its fall between marked intervals
  3. Record the time takes for the ball bearing to travel between the marks to calculate the velocity
  4. Repeat the test of accuracy and averages
  5. Create a velocity time graph
  6. The point at which the graph levels off indicates the terminal velocity of the ball bearing in the liquid
• Thinking distance is the distance travelled before the driver presses the break.


  Thinking distance = reaction time x velocity
• Stopping distance is the total distance travelled from seeing the hazard to stopping.


  Stopping distance = Thinking distance + Braking distance
• Braking distance is the distance travelled after the break is pressed until the vehicle stops


  Braking distance = $\frac{v^2}{2a}$
• A moment is the product of force and perpendicular distance from the pivot, measured in Newton-meters (Nm).


  M = F x d
• Principal of moments

  For a body in rotational equilibrium, the sum of the clockwise moments is equal to the sum of anticlockwise moments.
• A couple is two equal and opposite forces acting parallel to each other, creating torque
• Density is the ratio of mass to volume of a substance, measured in kilograms per meters cubed ($kg \space m^{-3}$)


  $\rho =$$\frac{m}{V}$
• An object with a lower density than the fluid will float
• An object with a higher density that the fluid will sink
• Pressure is the force exerted per unit cross-sectional area, measured in Pascals (Pa /Nm$^{-2}$ )


  P = $\frac{F}{A}$
• As depth increases, pressure increases due to the increasing weight of water above the point of measurement


  P = h $\rho$ g