1
Q
How to improve reliability in a method?
A
- Ensure 3 trials are done
- Try to reduce subjective measurements by using the same person for each test, or using data loggers/equipment that removes making a judgement.
2
Q
How to improve accuracy in a method?
A
- Use equipment with the best possible limit of reading and minimal uncertainty so measured results are as accurate as possible.
3
Q
How to improve the validity of a method?
A
- Insure independent and dependent variables can be used to test the aim of the experiment.
- Ensure all controlled variables are kept constant.
- Make sure that there are at least 5 changes in the IV.
- More controlled variables
4
Q
How can you define reliability?
A
The consistency of results
5
Q
How can you define accuracy?
A
How close do your measurements align with the true value.
6
Q
How can you define validity?
A
Is the experiment measuring what is intended.
7
Q
How to test if the results are reliable?
A
- Percentage range of trial date. Less than 10% percentage range within all results show reliability.
(Highest-Lowest / average) x 100 - Low scatter of points within a graph.
- Small error bars.
8
Q
How to test if the results are accurate?
A
- When a true value is provided, if the measured value is within 10% then it is accurate.
(experimental-true value / true value) x 100 - If the line of best fit passes through the origin.
This only works if the two values have a 0,0 relationship.
9
Q
How should you describe your IV?
A
- State what you are changing
- Explain what it is indicating of
10
Q
How should you describe your DV?
A
- The quantity you are measuring
- How you are measuring it
11
Q
How should you describe your CV?
A
- Identify the variable.
- Describe how you are going to control it.
- Identify the value you are going to set it at.
12
Q
How should you write your hypothesis?
A
Relate the IV to the DV. Example: As the IV (change made) the measured quantity (change observed) which indicates (effect of IV on DV)
13
Q
What should be included in your risk assessment?
A
- Identify: describe the risk
- Assess: assess the possible consequences
- Control: How will you take precautions to prevent it
14
Q
What is the limit of reading
A
- For any piece of equipment, the smallest increment it can measure is called the limit of reading and results should be measured to decimal place.
15
Q
What is uncertainty
A
- Uncertainty of measurement is a doubt we have in its magnitude. State the plus and minus margin that a measurement has.
16
Q
How to measure uncertainty
A
- With analogue instruments, the uncertainty is half the smallest value.
- With digital instruments, the uncertainty is one unit of the smallest decimal place.
17
Q
How to determine the gradient
A
- Pick two points from the line of best fit. The two points should be as far away from each other as possible.
- Draw a tringle using two dotted lines between the two points.
Use the “rise/run” formula to calculate the gradient.
18
Q
What units should you use for the line of best fit?
A
- M on vertical and s on horizontal = m/s or ms(-1)
- N on vertical and m on horizontal = N/m or Nm(-1)
- kg on vertical and ms(-2) on horizontal = kg/ms(-2) or kg m(-1) s(-2)
19
Q
What are systematic errors
A
- Same extent with each measurement
- Problems with the measuring equipment
- Can be reduced by calibrating instruments before use
20
Q
What are random errors
A
- Occurs in any measurement as a result of variations
- caused by unpredictable changes
- Can be reduced through repetition
21
Q
What are vectors and scalars
A
- Scalars are only described by a magnitude. (Time distance volume speed) To describe a scalar you need a magnitude and unit.
Vectors are described by magnitude and direction. (displacement, velocity, force, acceleration) To describe vectors you must have magnitude, unit and direction.
22
Q
Difference between speed and velocity
A
- Speed is the rate at which distance is travelled. Distance/time
- Velocity is the rate at which displacement changes.
displacement/time
23
Q
How to quickly convert from m/s to km/h
A
- 1 m/s is 3.6 km/h
- m/s to km/h (m/s x 3.6)
- km/h to m/s (km/h / 3.6)
24
Q
How to determine displacement from velocity-time graph.
A
- The area under the graph.
- Area above the x-axis is one direction
- Area under the x-axis in another
25
What is acceleration?
- Is the measure of the rates of change of velocity
- acceleration involves the change in velocity
26
v, u, a, t, s
v = final velocity
u = initial velocity
a = acceleration
t = time
s = displacement
27
How to find the resultant of two vectors
- Draw the first vector, and draw the second vector so that the head touches the tail. Draw an overall vector between the two.
- Use pythag, or trig to find the resultant
28
cosine and sine rule?
- c* = a* + b* - 2ab cos C
- a/sin A = b/sin b
29
What is the normal force
- The normal force acts perpendicular to the contact surface
30
How to get the weight of an object
W = m x g
g = 9.8
31
How are free-body diagrams drawn?
- use the middle of the object from the tail.
- force vectors show direction
- show the net force using a dotted line that is clearly labelled.
32
What is equilibrium
When the net force acting on an object is zero. It does not mean it is not in motion.
33
Newtwons 1st law
An object in constant motion or at rest will remain in constant motion or at rest unless acted upon by an unbalanced external force.
34
Newtons 2nd law
If there is a net force on an object it will undergo acceleration. F = ma
35
Newtons 3rd law
Every action has an equal and opposite reaction.
36
What is static friction and kinetic friction?
- Static: This is the friction you need to overcome to start an object moving.
- Kinetic: This is the friction present between to objects in relative motion
37
What is inertia?
The tendency of an object to keep doing what it was doing
38
What is momentum?
Momentum measures the inertia of moving objects.
p = mv
delta p / delta t = m x a
39
what is the law of conservation of momentum?
In an isolated system, the total momentum of the system is conserved. Not only does the magnitude stay the same, but so does direction.
delta p (a) + delta p (b) = 0
40
what is impulse?
Impulse is the change in momentum
delta p = F x t
41
what is the formula for gravitational potential energy
Ug = mgh
Ug = gravitational potential energy (J)
m = mass of object (kg)
g = gravitational acceleration (ms-2)
h = height above the earth
42
What is work?
When a force is exerted on an object and causes it to move.
W = F x s x cos(theta)
43
What is power
Power is the rate at which work is done
P = work/delta time (watt)
P = F x v
44
Energy time graphs
- The slope is power
- The area is work
Physics
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