physics

• Average Speed


  The total distance travelled divided by total time taken
• A speedometer doesn't show the average speed because the speed of the car changes from instant to instant, it only shows the instantaneous speed of the car
• Average speed


  The mean speed of the vehicle throughout a given period of time
• Distance = Speed x Time

  D/S/T triangle for rearranging equation
• Speed conversion


  Speed given in (m/s) can be converted to (km/h) by multiplying by 3.6
• Distance-time graph


  • Slope/gradient indicates the velocity - the steeper the slope, the quicker the car
  • Curve means the car is either accelerating or decelerating
• Displacement-time graph


  • Shows the distance travelled in a given direction (m)
  • Diagonal slope - moving
  • Horizontal line - constant speed
  • Negative diagonal slope - returning to starting point
• Displacement


  A vector quantity
• Velocity


  A vector quantity with magnitude and direction, measured in (m/s)
• Average velocity


  Calculated using displacement and time taken, measured in (m/s)
• Acceleration


  The rate at which velocity changes, measured in (m/s)²
• Velocity-time graph


  • Horizontal line - constant speed
  • Negative gradient - deceleration
  • Steep gradient - high acceleration
  • Shallow gradient - low acceleration
  • Area under graph - distance travelled
• Area of triangle = 1/2 base x height, area of trapezium = 1/2 (a+b) x height
• Force


  A vector quantity, the push or pull of one body on another, measured in newtons
• Types of forces


  • Weight (gravitational force)
  • Friction
  • Air resistance
  • Upthrust
  • Reaction force
  • Normal contact force
  • Water resistance
  • Thrust
• Friction


  The force that causes moving objects to slow down and stop, transfers kinetic energy to heat
• Resultant force


  The vector sum of two or more forces acting on an object
• Balanced forces


  • Forces acting on an object are equal in size and opposite in direction
  • Unbalanced forces cause an object to change its motion
• Newton's second law


  F=ma, force equals mass times acceleration
• Weight


  The force of gravity acting on an object, calculated as mass times gravitational field strength
• Mass


  The amount of matter an object is made up of, does not change with gravitational field strength
• Air resistance (drag)


  The force that acts against anything moving through air, depends on shape and speed
• Terminal velocity


  The maximum speed a falling object can reach when the upward drag force exactly balances the downward weight force
• Measuring average speed


  Use equipment to measure distance and time, repeat 3 times and take the average
• Improving measurement accuracy


  • Use fiducial markers, avoid parallax, use finer calibrations, repeat measurements
• Dependent variable


  Its value depends on changes in the independent variable, measured on the y-axis
• Independent variable


  Its value is independent of other variables, what is changed in the experiment, measured on the x-axis
• Hooke's law investigation


  Measure original spring length, add masses, measure extension, plot graph to check linearity and origin passing
• Hooke's law


  • Force is directly proportional to extension, linear graph passing through origin
  • Limit of proportionality - point where spring stops obeying Hooke's law
  • Elastic limit - maximum extension before permanent deformation
• Hooke's law does not apply to rubber bands, the force is not directly proportional to extension
• Turning effect (moment)


  Force x perpendicular distance from pivot, greater distance increases turning effect
• Balanced objects


  • No resultant force, clockwise moment = anticlockwise moment
• Centre of gravity


  The average location of the weight of an object, the weight force acts through this point
• Stability


  • Measure of how likely an object is to topple over, depends on centre of gravity position and base width
• Center of gravity


  The point at which the weight of an object is concentrated
• When an object is pivoted through its center of gravity, it will be balanced if there are no other forces other than the weight of the object because the mass of the object is equally spread out through its length
• The weight force acts through the center of gravity
• When an object is not pivoted through its center of gravity, the weight will produce a turning effect
• Stability


  A measure of how likely it is for an object to topple over when pushed or moved
• The position of the center of gravity will affect stability