Definitions

Question 1

Average speed

Answer 1

Total distance travelled per unit of time.
Assumes that an object moves at the same speed throughout the entire distance.

Question 2

Instantaneous speed

Answer 2

The speed of an object at a particular instant.

Question 3

Velocity

Answer 3

The rate of change in displacement

Question 4

Acceleration

Answer 4

Rate of change of velocity

Question 5

scalar quantities

Answer 5

Physical quantities that only have a magnitude

Question 6

vector quantities

Answer 6

Physical quantities that have both magnitude and direction

Question 7

mass

Answer 7

measure of amount of matter in a body

Question 8

weight

Answer 8

gravtional force acting on an object that has mass

Question 9

gravitational field

Answer 9

region in which a mass experiences a force due to gravitational attraction

Question 10

gravitational field strength

Answer 10

gravitational force per unit mass placed at that point

Question 11

Differences between mass and weight

Answer 11

Mass:
- measure of amount of matter in body
- scalar quantity
- independent of gravitational field strength
SI unit: kg

Weight:
- gravitational force acting on an object that has mass
- vector quantity
- dependent of gravitational field strength
- SI unit: N

Question 12

Newton’s First Law of motion

Answer 12

every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it

Question 13

Newton’s First Law of motion relation to inertia (+ definition of inertia)

Answer 13

• inertia of object refers to reluctance of the object to change its state of rest or motion, due to mass
• greater mass –> greater inertia
• larger mass –> harder for object to start moving; slow down; move faster; change direction

Question 14

Newton’s Second Law of motion

Answer 14

acceleration of object directly proportional to net force acting on it, inversely proportion to mass. Accelerates in direction of net force

Question 15

Newton’s Third Law of motion

Answer 15

If body A exerts a force on body B, body B will exert an equal and opposite force on body A
Note: pair of objects physically interacting (not necessarily in contact)

Question 16

Friction

Answer 16

Contact force that opposes or tends to oppose motion between surfaces in contact

Question 17

Positive effects of friction

Answer 17

• walk
• slow down moving objects (e.g. brakes in cars)
• grip (e.g. prevents skidding of cars, rock climbers use chalk powder)

Question 18

negative effects of friction

Answer 18

• wear & tear (tyres/shoes)
• unwanted slowing down/stopping of motion
• generate unwanted heat (machinery, large amt of energy transferred to surroundings as heat)

Question 19

reducing negative effects of friction

Answer 19

• smooth & polished surfaces
• wheels & rollers
• lubricants
• adopt a streamline shape

Question 20

how do objects fall with air resistance

Answer 20

• air resistance increases as falling speed increases
• air resistance = weight –> zero acceleration –> terminal velocity

Question 21

what are the factors that affect terminal velocity and how do they affect

Answer 21

weight:
- larger weight –> larger air resistance to balance weight
- accelerates for longer duration –> larger terminal velocity
- Reach ground in shorter time for same height due to larger average speed

surface area:
- larger SA –> trap more air molecules underneath
- accelerates for shorter duration –> smaller terminal velocity
- reach ground in a longer time for same height due to smaller average speed

Question 22

moment

Answer 22

product of force and perpendicular distance from the pivot to the line of action of the force

Question 23

center of gravity

Answer 23

point at which weight of object appears to act

Question 24

how is equilibrium reached (in terms of moments)

Answer 24

1: resultant force on object is 0
2: resultant moment about any point on object is zero

Question 25

Principle of Moments

Answer 25

For an object in equilibrium, the sum of any clockwise moments about any point is equal to sum of anti-clockwise moments about the same point

Question 26

stability

Answer 26

ability to return to original position after slightly displaced

Question 27

how to increase stability

Answer 27

- increase base area - lower center of gravity line of action of weight acts within base area of object --> restoring moment when tilted

Question 28

kinetic particle model of matter

Answer 28

all matter is made up of tiny particles which are in continuous random motion

Question 29

kinetic store

Answer 29

associated with motion

Question 30

gravitational store

Answer 30

associated with position (height) of objects relative to a reference level

Question 31

elastic potential store

Answer 31

associated with objects which are stretched/compressed

Question 32

chemical potential store

Answer 32

associated with bonds of chemical compounds, can be released through chemical reactions

Question 33

internal energy

Answer 33

sum of KE due to random motion of particles and potential energy due to forces of attraction between particles

Question 34

nuclear store

Answer 34

associated with energy in nucleus of atom

Question 35

principle of conservation of energy

Answer 35

energy neither created nor destroyed but can be transferred from one body to another or converted from one form to another. Total energy in an isolated system is constant

Question 36

power

Answer 36

rate of work done/energy transfer

Question 37

adv and disadv of fossil fuels

Answer 37

adv: - cheaper - high reliability in supplying uninterrupted power disadv: - extensive mining --> negative impact on ecosystem - burning results in air pollution & greenhouse gases --> global warming

Question 38

adv and disadv nuclear fuel

Answer 38

adv: - high efficieny - high reliability in supplying uninterrupted power - low carbon energy source --> reduce greenhouse gas emissions disadv: - additional cost needed to dispose radioactive waste - waste from uranium minign can contaminate groundwater & surface water sources - risk of nuclear accidents

Question 39

adv and disadv biofuel

Answer 39

adv: - cheaper - widely available disadv: - produce greenhouse gases that cause global warming

Question 40

adv and disadv wind

Answer 40

adv: - cost effective - clean energy as no harmful gases produced disadv: - intermittent power as not easy to find places where there is a steady wind blowing at speed of 20-25km/h - noise pollution, loss of habitat

Question 41

adv and disadv tides

Answer 41

adv: - more reliable than wind/sun - clean energy as no harmful gases produced disadv: - high cost of building tidal barrages - tidal barrage systems can disrupt ecosystems

Question 42

density

Answer 42

mass per unit volume

Question 43

pressure

Answer 43

force per unit area

Question 44

how much does atmospheric pressure decrease with altitude

Answer 44

drops by half every 5.6km