Spec Point P4.2.1
What is the equation that links average speed, distance and time?
Avg. Speed (m/s) = Distance (m) / Time (s)
v = s/t
Spec Point P4.2.2
What are the typical speeds of wind, sound, walking, running, cycling, driving in built-up area, driving on motorway & trains?
- Wind = 7m/s
- Sound = 340m/s
- Walking = 1.4m/s
- Running = 3m/s
- Cycling = 5.5m/s
- Cars in built up area = 13m/s
- Cars on motorway = 30m/s
- Trains = up to 55m/s
Spec Point P4.2.3
a) How do you make measurements of distance & time?
- For distance, measuring item should be longer than distance measured
- For shorter distances, use a ruler/metre stick
- For longer distances, like how far someone walks, use a rolling tape measure
- To measure longer times, use a stopwatch
- For short times, use light gates connected to datalogger - stopwatches involve human error like reaction times
Spec Point P4.2.3
b) Describe an experiment to measure the speed of a trolley down a ramp
- Set up ramp & runway
- Mark a line on ramp so trolley starts at same point each time
- Set up light gates directly after start line, at end of ramp & end of runway
- Connect light gates to datalogger to record time to pass between them
- Measure distance between light gates using ruler
- Let trolley roll down ramp to end of runway - record time between 1&2, 2&3
- Repeat & take avg. time
- Calculate speed using v=s/t
- You could change material on ramp & runway to investigate friction, or change angle on ramp
Spec Point P4.2.4
How can you convert between units?
- Km/h - m/s = divide by 3.6
- Hours to seconds = multiply by 3600
Spec Point P4.2.5
What is the difference between a scalar & a vector?
- Scalar - a quantity with only magnitude
- Vector - a quantity with magnitude & direction
- E.g. displacement & distance - distance is scalar, displacement is vector
- E.g. speed & velocity - speed is scalar, velocity is vector
Spec Point P4.2.6
a) What is the equation linking acceleration, change in speed & time?
Acceleration (m/s^2) = Change in Speed (m/s) / Time (s)
Spec Point P4.2.6
b) Describe an experiment to measure the acceleration of a trolley down a ramp
- Repeat experiment used to find speed
- Set up light gates to record speed & time
- Speed at gate 2 = change in speed down ramp
- Speed at gate 3 = change in speed down ramp & runway
- Use acceleration equation
Spec Point P4.2.8+9
How can you interpret distance-time graphs?
- Gradient = avg. speed
- Steeper = faster
- Flat sections = stationary
- Straight uphill = constant speed
- Steepening curve = acceleration
- Levelling curve = deceleration
- To find speed on curve, draw tangent & find gradient
Spec Point P4.2.8+9+10
How can you interpret velocity-time graphs?
- Gradient = avg. acceleration
- Steeper = greater acceleration
- Flat = constant velocity
- Straight uphill = acceleration
- Straight downhill = deceleration
- Curve = changing acceleration
- Area under graph = distance travelled
- To find area under curved section, count squares
Spec Point P4.2.11
What is the value of acceleration in free-fall?
10m/s^2
Spec Point P4.3.1
What is resultant force?
- Resultant force - the sum of all individual forces acting on object
- E.g apple on table - force due to gravity acts downwards, normal contact force pushes up on apple - forces are equal - apple in equilibrium
- E.g. accelerating block - weight & NCF are equal, but driving force is greater than friction - block moves forwards
Spec Point P4.3.3
Spec Point P4.3.3
