Week 1 - Uncertainties in Scientific Measurements

Question 1

Define Measurement

Answer 1

Gives a property and number to something.
eg. 2 metres

Question 2

What could be mistaken for ‘measurements’, but are not?

(3)

Answer 2

Comparisons (2 pieces of string)
Counting
Tests (normally lead to a yes/no answer or a pass/fail answer)

Question 3

What are the 3 fundamental quantities; describe them and their significance

(3)

Answer 3

Length
Mass
Time
Significant as all other physical quantities can be constructed from these 3

Question 4

What are all the fundamental units of measurement and their SI unit?

(8)

Answer 4

Length (m, metre)
Time (s, second)
Mass (kg, kilogram)
Current (A, ampere)
Temperature (oC, celcius)
Thermodynamic temperature (K, Kelvin)
Amount of substance (mol, mole)
Luminous intensity (cd, candela)

Question 5

What are the quantities of motion; describe their significance.

(3)

Answer 5

Displacement
Velocity
Acceleration
Significant as these concepts can be used to study all objects in motion (provide the basis for)

Question 6

Define Displacement; SI Unit and TYPE of quantity

Answer 6

Change in position; SI Unit is M, Metre.
Vector quantity - requires both magnitude and direction to fully describe it

Question 7

2 factors

Define a vector quantity; provide example

Answer 7

A quantity that requires both magnitude and direction to completely describe it;
eg. displacement

Question 8

1 factor

Define a scalar quantity; provide example

Answer 8

A quantity completely described by magnitude alone;
eg. time, weight

Question 9

Define speed; what type of quantity is it and why?

Answer 9

Defined as total distance of an object / total time elapsed; scalar quantity - does not need direction to describe it

Question 10

Define velocity; the formula, SI Unit; type of quantity and why?

Answer 10

The rate at which displacement occurs (the change in object’s position);
displacement/time;
m/s;
vector quantity - needs both direction and magnitude to describe it

Question 11

Describe the difference between speed and velocity using an example of 2 cars that travel the same distance.
Car 1 - directly from point A to B
Car 2 - wavey motion from point A to B

Answer 11

Car 1 and 2 both have the same average velocity - as they have the same displacement in the same interval (change in displacement/change in time)

Speed of Car 2 is greater as it has travelled a GREATER distance than Car 1
Speed = total distance/total time

Question 12

Describe the difference in displacement and distance; give an example

Answer 12

Displacement is the change in POSITION of an object (vector quantity); distance is length between objects/points that DOES NOT REGARD DIRECTION (scalar quantity)
eg. Throwing a ball up in air and catching it; distance is x metres, displacement is 0

Question 13

be specific

Define acceleration; unit and quantity type

type of change

Answer 13

Change in velocity (non-uniform; meaning change in speed) over time; m/s^2; vector quantity

Question 14

Acceleration interpretation: sign of velocity and acceleration are the SAME
V= inc.
a= uniform (unchanging)

Answer 14

speed will be increasing; displacement over time is increasing = VELOCITY

speeding up, foot on the gas

Question 15

**

Acceleration interpretation: sign of velocity and acceleration are DIFFERENT
V = inc.
a = uniform (stays unchanging

Answer 15

speed is decreasing;
eg. displacement over time is decreasing = VELOCITY; acceleration is uniform (unchanging speed)

breaking, slowing down

Question 16

what DOESNT this effect?

What does + / - in velocity symbolise?

Answer 16

direction of the displacement; + (moving right along x-axis) and - (moving along left of x-axis)

Doesn’t effect time; will always be positive

Question 17

How do you quantify an uncertainity in measurement; describe them.

(2)

Answer 17

width of margin/interval
confidence level - states how sure you are that we have the ture value within the margin

Question 18

Where would you need to have a measurement of uncertainity?

(3)

Answer 18

Calibration - where uncertanity measurement must be reported
Test - needed to measure a pass/fail
Tolerance - need to know uncertainity BEFORE deciding if tolerance is met or not

Question 19

Define the limit of precision

Answer 19

The smallest set of marks on a particular device that cna be used to make a measurement

Question 20

Define absolute uncertainity

Answer 20

The limit of precision divided in 2
eg. l.o.p=1cm
absol uncer = +/- 0.5cm

Question 21

Define the equation used to find the percentile of absolute uncertainity

Answer 21

% abs. uncer = abs.uncer/length x100

eg. height = 7.2cm
abs. uncer = +/- 0.5cm
= 0.5/7.2x100 = 6.94%