y9 physics

• Contact forces


  Forces that require two objects to be touching for the force to act
• Non-contact forces


  Forces that do not require the objects to be touching for the force to act
• Contact forces


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


  • Magnetic forces, gravitational forces, electrostatic forces
• Force


  A push or pull acting on an object due to an interaction with another object
• When two objects interact, there is a force produced on both objects
• Interaction pair


  A pair of forces that are equal and opposite and act on two interacting objects
• Gravitational force acts on all masses, but is only noticeable for very large masses like planets
• Weight


  The force acting on an object due to gravity (the pull of the gravitational force on the object)
• Mass


  The amount of stuff in an object, which has the same value anywhere in the universe
• As the mass of an object increases

  The weight of the object increases proportionally
• The weight of an object changes with its location due to variations in gravitational field strength
• Resultant force


  The single force that has the same effect as all the individual forces acting on an object
• Determining the resultant force

  Set a direction as positive, add all forces in that direction, subtract all forces in the opposite direction
• Work done


  The energy transferred when a force acts on an object through a distance
• 1 joule of work is done when a force of 1 newton causes an object to move 1 metre</b>
• Work done against friction

  Can cause a rise in the temperature of the object and surroundings
• Elastic deformation


  When an object can return to its original shape after a force is removed
• Inelastic deformation


  When an object does not return to its original shape after a force is removed
• Hooke's law


  The extension of a stretched spring is directly proportional to the force applied, up to the limit of proportionality
• Work is done on a spring when it is stretched or compressed, and this energy is stored in the spring's elastic potential energy store
• Hooke's law


  F = ke, where F is the force, k is the spring constant, and e is the extension or compression
• Hooke's law


  • Applies when the object is not stretched or compressed past its limit of proportionality
  • All work done on a spring is transferred to its elastic potential energy store
• Calculating elastic potential energy


  E = 1/2 kx^2, where E is the elastic potential energy, k is the spring constant, and x is the extension or compression
• The work done, or energy stored in the elastic potential energy store, for a particular force (or extension) can also be found by calculating the area under the linear force-extension graph up to that force (or extension)
• When the line of best fit is a straight line, it means there is a linear relationship between force and extension (they're directly proportional)
• When the line begins to bend, the relationship between force and extension becomes non-linear - the spring stretches more for each unit increase in force
• The point where the line starts to curve is the spring's limit of proportionality
• Upthrust


  The force that pushes up on an object submerged in a fluid, equal to the weight of fluid displaced
• An object floats if the upthrust is equal to its weight, and sinks if its weight is greater than the upthrust
• An object less dense than the fluid it's in will float, while an object denser than the fluid will sink
• Distance


  How far an object has moved
• Displacement


  The distance and direction an object has moved relative to a starting point (vector quantity)
• Speed


  How fast an object is moving (scalar quantity)
• Velocity


  How fast an object is moving and in which direction (vector quantity)
• Acceleration


  How quickly an object's velocity is changing
• Calculating acceleration


  a = (v_final - v_initial) / t, where a is acceleration, v_final is final velocity, v_initial is initial velocity, and t is time
• A negative acceleration is a deceleration
• Acceleration has units of m/s^2, different from the units for speed and velocity (m/s)
• Acceleration


  The rate of change of velocity