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P1 (Speed and velocity, Forces, Mass, weight and density, Moments,…

- - - - Only works when object is moving at a constant speed
    - - Because it only contains a magnitude (without direction)
  - - - Average speed = distance treveled. / time taken
  - - - Velocity (m/s) = displacement (m) / time (s)
  - - - if object is moving at a constant speed
        
        Straight line represents constant speed
      - How large or small the speed is
        
        A steep slope means object is moving at a large speed
        
        Shallow slope means object is moving at a small speed
      - Stationary object
        
        Flat, horizontal line
    - - Objects might be moving at changing speed, represented by a curve
        
        Slope of line will be changing
        
        If slope increases, speed increases (acceleration)
        
        If slope is decreasing, speed is decreasing (decelerating)
    - - Speed of moving object can be calculated from gradient of line on a distance-time graph
        
        Make sure to convert for distance and time to standard units
  - - - If object is moving
        
        with a constant acceleration or deceleration
        
        Straight line represents constant acceleration
      - Magnitude of acceleration or deceleration
        
        Slope represents magnitude of acceleration
        
        Steep slope means large acceleration (or deceleration) - i.e. object's speed changes very quickly
        
        Gentle slope means small acceleration (or deceleration) - i.e. the object's speed changes very gradually
        
        Flat line means acceleration = zero - i.e. object is moving with constant speed
      - Distance travelled by object can be found by determining area beneath graph
        
        If area beneath graph forms triangle, area can be determined using
        
        area = 1/2 x base x height
        
        If area beneath graph is a rectangle, area can be determined using
        
        area = base x height
    - - Acceleration of an object can be calculated from gradient of a speed-time graph
  - - - is found by the difference between initial and final velocity
      - Change in velocity = final velocity - initial velocity
    - - Acceleration (m/s^2) = Change in velocity (m/s) / change in time (s)
    - - Describes how much an object's velocity changes every second
  - - - Weight = mass x gravitational strength
    - - Object falling through fluid experiences two forces
        
        Weight
        
        Friction
      - skydiver example
        
        Force of air resistance acting on skydiver increases with speed
        
        Eventually force of air resistance equals weight and forces become balanced
        
        Means the acceleration of skydiver is zero and they are travelling at terminal velocity
        
        When skydiver opens the parachute, air resistance increases and slows down acceleration
        
        skydiver decelerates, eventually forces balance out again and new slower terminal velocity is reached
- - - - F = ma
  - - - F = kx
        
        F - force applied
        
        k - spring constant
        
        Force per unit of extension
        
        Spring constant measure how stiff spring is
        
        x - extension of spring
    - - Objects extending beyond limit of proportionality no longer obey hooke's law and will no longer return to original length
  - - - Direction which the object will move as a result of all of forces
      - Magnitude of final force experiences by the object
      - Forces can combine to produce
        
        balanced
        
        Forces have combined in a way that they cancel each other out and no resultant force acts on the body
        
        unbalanced forces
        
        Forces have combined in such way that they do not cancel out completely and there is a resultant force on the object
  - - - Object will continue moving at same velocity if it was moving
    - - Speed of object can change
      - Direction of object can change
  - - - Speed of object moving in circle must be constant
        
        travelling at the same distance every second
      - Direction of travel is always changing as the object moves along circular path
    - - force will cause that object to change direction
      - If force continues to act at 90 degrees to motion, object will keep changing direction and travel in circle
        
        this is what happens when a planet orbits a star
    - - Mass of object
        
        Greater mass requires greater force when speed and radius are constant
      - Speed of object
        
        Faster moving objects require greater force when mass and radius are constant
      - Radius of the circle
        
        Smaller radius requires greater force to keep speed and radius constant
  - - - Change in speed
        
        forces can cause bodies to speed up or slow down
      - Change in direction
        
        Forces can cause bodies to change their direction of travel
      - Changes in shape
        
        Forces can cause bodies to stretch, compress, or deform
  - - - Friction is a force that works in opposition to motion of an object
        
        slows down the object + increases thermal energy
        
        Caused by imperfections in surfaces of objects moving over another
      - When friction is present, energy is transferred in form of heat
        
        Raises the temperature (thermal energy) of object and its surroundings
        
        Work done against frictional forces causes this rise in temperature
    - - Friction acts on objects moving through gasses and liquids as the particles collide with the object
        
        This type of friction is drag
      - Air resistance is a type of friction that slows motion of an object
        
        Particles bump into the object as it moves throught the air
        
        As a result, the object heats up due to the work done against frictional forces
- - - - it is unchanged by the object's location
  - - - Different planets have different gravitational strength
    - - Objects stay firmly on the ground
      - Objects will always fall to the ground
      - satellites are kept in orbit
  - - - Also known as acceleration or free fall or acceleration due to gravity
  - - - Objects made from low density materials have low mass
      - Similarly sized objects made from high density materials have high mass
    - - P = m/v
    - - If mass is measured in g and volume in cm^3, density will be g/cm^3
      - If mass is measured in kg and volume in m^3, density will be kg/m^3
    - - Measuring density of regularly shaped objects
        
        1) Place object on a digital balance and note down its mass
        
        2) Use either ruler, vernier calipers or micrometer to measure objects dimensions (width, height, length and radius)
        
        3) repeat measurements and take average of these readings before calculating density
      - Measuring density of irregularly shaped objects
        
        1) Place the object on a digital balance and note down its mass
        
        2) Fill the eureka can with water up to a point just below the spout
        
        3) Place an empty measuring cylinder below its spout
        
        4) Carefully lower the object into the eureka can
        
        5) Measure the volume of the displaced water in the measuring cylinder
        
        6) Repeat these measurements and take an average before calculating the density
      - Density of liquid
        
        1) Place an empty measuring cylinder on a digital balance and note down the mass
        
        2) Fill the cylinder with the liquid and note down the volume
        
        3) Note down the new reading on the digital balance
        
        4) Repeat these measurements and take an average before calculating the density
    - - Liquid with lower density will float on a liquid with higher density if liquids do not mix
- - - - Example: Rotation caused by a force is one side of a pivot (fixed point that object can rotate around)
        
        can either be clockwise or anticlockwise
    - - Moment (M) = Force (F) x perpendicular distance of force to pivot (d)
    - - If an object is balanced, total clockwise moment about a pivot equals anticlockwise movement about that pivot
  - - - If object is moving it will continue to move in a straight line
      - Will remain stationary if stationary
      - Will also not start or stop turning
    - - Forces on object must be balanced
      - There must be no resultant force
  - - - Object is stable when its centre of gravity lies above its base
        
        Narrower base object has, higher centre of gravity and object is more likely to topple over if pushed
      - Wider base an object has, lower centre of gravity and it is more stable
        
        Position of centre of gravity of an object affects its stability
- - - - object at rest has no momentum
      - Momentum keeps object moving in same direction making it difficult to change direction of an object with large momentum
    - - Momentum (p) = mass (m) x velocity (v)
    - - Object traveling to the right has a positive momentum
      - Object traveling in opposite direction (to the left) will have negative momentum
    - - Object accelerates or decelerates
      - Change direction
      - Mass changes
  - - - means energy within system is constant and there is an absence of external forces (e.g. friction)
    - - Certain number of objects under consideration, this can be one object or multiple objects