Motions and Forces

• Distance time graphs tell us how far something has travelled in a certain period of time
• the gradient of the line at any point on q distance time graph tells you the speed the object is travelling. The gradient is equal to the speed
• an upwards or downwards straight line on a distance time graph tells us the object is moving at a constant speed
• a flat line on a distance time graph tells us the object is stationary
• an upwards curve on a distance time graphs tells us the object is accelerating
• a downwards curve on a distance time graph tells us the object is decelerating
• to find the speed at a curved section, you have to draw a tangent at the curved part .You then pick two points and calculate the change in distance and the change in time between the two points.
• on a velocity time graph, to find the gradient you do the

  change in velocity / change in time

  (acceleration equation)
• on a velocity time graph, the gradient tells us the acceleration or deceleration of the object
• to find the distance travelled on a velocity time graph, you need to find the area under the curve
• when the distance has been found on a velocity time graph, leave the answers in metres, not metres-squared
• when asked to find the area under the curve on a velocity time graph, count up the squares on the grid background.
• an upwards straight line on a velocity time graph tells us the object is at a constant acceleration
• a downward straight line on a velocity time graph tells us that the object is at a constant deceleration
• a flat line on a velocity time graph tells us the object is at a constant velocity
• an upwards curve on a velocity time graph tells us the rate of acceleration increasing
• a downwards curve on a velocity time graph shows us that the rate of acceleration is decreasing
• scalar quantities just have magnitude

  vector quantities have magnitude and direction
• speed is a scalar quantity because it just has how fast you are going (magnitude)
• velocity is a vector quantity because it is how fast you are going in a certain (magnitude and direction)
• the equation for speed is

  speed=distance/time
• the equation for acceleration is

  (end speed - start speed) / time
• The speed of sound in air is 330 m/s
• to determine the average speed of a toy car along a ramp:

  speed = distance/time so-

  • measure the distance toy the car travels the distance using a tape measure
  • time how long it takes for the car to travel the distance using a stop clock
  • divide the distance by time to get the speed
  • repeat and find the mean
• to determine acceleration in the lab:

  acceleration - (end speed-start speed) / time taken

  • place two light gates a distance apart to measure the start and end speed of the object
  • the light gates will also measure the time taken to change speed
  • calculate the change in speed by : end speed - start speed
  • divide the change in speed by time taken to find the acceleration
  • repeat and find the mean
• when forces are balanced, there is zero resultant force, so there will be no change in motion
• when forces are unbalanced, there will be a resultant force and motion will change
• ( A toy car has a mass of 100g. The toy car accelerates at 2.0 m/s^2. Calculate the force producing this acceleration)

  Acceleration =(end speed - start speed) / time taken so:

  • place two light gates at a distance apart to measure the start and end speed of the object
  • the light gates will also measure the time taken to change speed
  • calculate the change in speed by: end speed - start speed
  • divide change in speed my time taken to find the acceleration
  • add mass to the trolley and repeat
  • force = mass x acceleration
  • mass = 100g
  • acceleration = 2m/s^2
  • 100g/1000=0.1kg
  • force=0.1 x 2
  • force = 0.2
• the piece of equipment is newton metre
• the unit for weight is Newtons
• the factors that affect braking distance are

  • the condition of the road, tyres and brakes
  • the mass of the vehicle
  • the weather
  • the speed of the vehicle
• the factors affecting thinking distance are

  if the driver is tired, distracted, alcohol, drugs