Motion,forces and energy

• the SI units for:

  mass --> kilogram

  length --> meter

  time --> seconds
• time is measured using 3 instruments:

  stopwatch,clock, and timer
• to measure the period of a single oscillation :

  1. measure the time taken for multiple oscillations
  2. take the average for a single osicalltion
• the 3 main measuring instruments for mass are : top-pan balance, springe balance and beam balance
• to measure the mass of a liquid

  1. measure the mass of the empty container
  2. measure the mass of the conatiner with the liquid
  3. find the difference between the masses
• length is measured using mainly 3 instruments: meter rule, measuring tape and micrometer
• to measure curved lines:

  1. lay a thread along the curved line
  2. mark on the thread the begining and ending of the thread
  3. using a ruler measure the distance between the Marks
• to measure extremely short distance/ the thickness of a sheet of paper without using a micrometer:

  1. measure the thickness of stack of papers
  2. take the average thickness
• SI unit for volume --> meter cubed (m3)
• formula to measure the volume of regular shapes :

  Base area x height
• the volume of liquids or any solids that flow like a liquid is done using a measuring cylinder
• to measure the volume of an irregular shape using the displacement method:

  1. place a fixed volume of water into a measuring cylinder
  2. slowly, fully immerse the irregular solid into the water
  3. the difference between the initial and final volume is the volume of the object
• sources of error and their prevention include:

  1. Zero error - find the difference between the initial and final reading
  2. parallax error - the eyesight must be perpendicular to the scale
  3. meniscus error - always taking reading of the bottom of the meniscus
• types of quantities:

  1. scalar quantity --> has magnitude only
  2. vector quantity --> has both magnitude and direction
• distance, speed , time , mass, energy and temperature are all example of scalar quantites
• density is mass per unit volume
• formula of density:

  density = mass/volume
• speed is distance travelled per unit time
• formula of speed:

  speed = distance/ time
• velocity is the distance travelled per unit time at a given direction
• acceleration is the change in velocity per unit time
• unit for speed or velocity: m/s or km/h
• unit for acceleration : m/s2
• formula for accelertion:

  acceleration = change in velocity/ time
• the slope/gradient of a line in a distance-time graph represents the speed
• A--> at rest / stationery

  B--> constant speed

  C--> acceleration

  D--> deceleration

  
• the area under a speed - time graph represent the distance travelled
• the gradient/ slope of a speed-time graph represents the acceleration
• `1--> constant acceleration

  2--> constant speed

  3--> constant deceleration

  
• A-->decreasing acceleration

  B--> increasing acceleration

  
• g-->decreasing deceleration

  h--> Increasing deceleration

  
• force,weight,velocity , acceleration and momentum are all examples of vector quantities
• mass is a measure of the quantity of matter in an object at rest relative to the observer
• weight is a gravitational force on an object that has mass
• A force is a push or a pull

  When a force is applied on an abject it can change it shape,size, speed and direction but it can't change its mass
• Types of forces including resisting forces (like air resistance, drag and friciton) , weight, tension, normal contact and water upthrust
• Gravitational field strength is the force per unit mass and is equivalent to the acceleration of free fall in a vacuum

  Weight = gravitational field strength x mass
• Resultant force is a single force that has the same effected as all other forces applied combined

  When forces act along the same line:

  If the forces act in the same direction→ the resultant forcce is the sum of all the forces

  If the forces are acting in different direction → the resultant force is the difference of in different direction

   Resultant force = mass x acceleration
• • Where ever there is a resultant force, there is acceleration(speeding up, slowing down and changing direction)
  • If the resultant force is zero it is either the object is at rest or moving at constant speed
• Solid friction is the force between two surfaces that may impede motion and produce heat, it called drag and it occurs when an object travels through matter