physics 2

• Vector quantities 


  have a magnitude and a direction

  e.g. force, velocity, displacement, acceleration
• Scalar quantities 


  some quantities have a magnitude but no direction

  e.g. speed, distance, mass, temperature, time
• How are vectors usually represented

  by an arrow

  length of arrow shows magnitude

  direction of arrow shows direction of quantity
• Force


  push or pull that’s acts on an object
• Contact force 


  when 2 objects have to be touching for a force to act

  e.g. air resistance, tension, friction
• Non-contact force 


  if objects don’t need to be touching for the force to act

  e.g. gravitational force, magnetic force
• Interaction force 


  when 2 objects interact, a force is produced on both objects. The forces on the 2 objects are equal in size but act in opposite directions

  e.g. gravitation attraction between earth and the sun
• Mass


  amount of matter in an object

  scientists sometimes think all of the mass in an object as being at one single point of an object - centre of mass
• Weight


  The force (caused by gravitation girl around the Earth) acting in an object due to gravity

  weight of an object depends on its mass and the strength of the gravitational field it’s in

  can be measured with a calibrated spring balance
• when force moves to an object through a distance energy is transferred and work is done on the object
• Resultant force


  if a number of forces act at a single point you can replace them with a single force
• Inelastically deformed 


  if object doesn’t go back to how it was
• Elastic objects


  objects that can be elastically deformed
• when you apply force to an object you may cause it to deform
• 1. measure mass of each mass
  2. calculate its weight
  3. measure original length of spring
  4. add mass to spring and allow it to come to rest
  5. record force and measure new length of spring
  6. repeat steps 5-7 times until you’ve added all the masses
• Distance


  how far an object has moved

  scalar quantity so doesn’t involve direction
• Displacement 


  vector quantity

  measured distance and direction in a straight line from an objects starting point to its finishing point
• Speed 


  scalar

  how fast you’re going with no regard to the direction
• Velocity


  vector

  speed in a given direction
• typical speeds of objects:

  • walking 1.5m/s
  • running 3m/s
  • cycling 6m/s
  • car 25m/s
  • train 30m/s
  • plane 250m/s
  • sound in air 330m/s
• Speed depends on persons:

  fitness

  age

  terrain
• Uniform acceleration 


  speeding up at constant rate
• Acceleration 


  change in velocity in certain amount of time
• ~


  approximate answer!!!
• Drag


  resistance you get in a fluid (gas and liquid)

  acts in the opposite direction to the movement of the object

  increases as speed of the object increases
• terminal velocity 


  when object starts falling the force of gravity is much larger than the drag slowing it down

  this means object accelerates

  as speed increases so does drag

  this reduces acceleration until drag is equal to the gravitation force

  resultant force on object is then zero

  the object will fall at a constant speed
• Newtons law


  If resultant force on stationary object is zero the object will remain stationary. If resultant force on a moving object is zero it'll just carry on moving at the same velocity
• Newton’s second law


  acceleration is inversely proportional to the mass of an object so an object with a larger mass will accelerate less than one with a smaller mass for a given force

  force acting in an object and acceleration of the object are directly proportional
• Newton’s third law


  when 2 objects interact the forces they exert in each other are equal and opposite
• Mass being accelerated


  • Total mass of trolley, hook and added masses
• Force causing acceleration


  Weight of the hook and the masses on the hook
• Finding the force


  1. Measure the mass of the hook and any masses on the hook

  2. Multiply this by g
• Finding the acceleration


  1. Mark a starting line on the table the trolley is on

  2. Place the trolley on the starting line

  3. Hold the trolley so the string is tight and not touching the table then release it

  4. Record acceleration measured by the light gate as the trolley passes through it
• investigating how force affects acceleration

  1. start will all extra masses loaded onto trolley
  2. moving masses from trolley to the hook will keep the total mass the same
  3. but it will increase the force
  4. each time you move a mass record a new force and measure acceleration
  5. you should find that as force goes up the acceleration goes up
• thinking distance


  how far vehicle travels during drivers reaction time

  the reaction time is the time between the driving seeing a hazard and applying the breaks
• Breaking distance


  distance taken to stop under the breaking force
• Thinking distance affected by

  speed - faster you’re going, further you’ll travel during the time you take to react

  reaction time - longer your reaction time the longer your thinking distance
• Drivers reaction time affected by

  tiredness

  drugs

  distraction

  alcohol
• Driving while tired


  makes you slower to react

  increases your reaction time which increases your thinking distance

  means your stopping distance is longer so you’re more likely to crash
• Braking distance affected by

  speed - for given braking force, the faster the vehicle travels the longer ur takes to stop

  weather/road surface - if there’s less grip between vehicles tires and road it can cause the vehicle to skid

  skidding increases braking distance of a car

  water, ice, oil or leaves in road all reduce grip