*9 Application of Force and Transfer of Energy

Question 1

What are the two types of forces?

Answer 1

Contact force
Non-contact force

A contact force is a type of force that occurs when two objects are in direct physical contact with each other.
A non-contact force is a force which acts on an object without coming physically in contact with it.

Question 2

What are contact forces?

Answer 2

Forces that acts between 2 objects in physical contact.

examples of contact forces

Question 3

What are non-contact forces?

Answer 3

Forces that acts between 2 objects not touching each other.

examples of non-contact forces

Question 4

Give 2 examples of contact forces.

Answer 4

1. friction
2. elastic force

Question 5

Give 2 examples of non-contact forces.

Answer 5

1. gravitational force (weight)
2. magnetic force

Question 6

State how magnetic force works between 2 unlike poles.

Answer 6

They attract each other.

Question 7

State how magnetic force works between 2 like poles.

Answer 7

They repel each other.

Question 8

What is the SI unit of force?

Answer 8

newton (N)

Question 9

What is weight?

Answer 9

It measures the amount of gravitational force on an object.

Question 10

What is mass?

Answer 10

The amount of matter in a body.

Question 11

What is the SI unit of mass?

Answer 11

kilogram (kg)

Question 12

List down 4 differences between mass and weight.

What are they?
Their SI units
Do they change with location?
What is used to measure them?

Answer 12

1) Mass is the amount of matter in a body. Weight is the gravitational force exerted at an object.
2) SI unit of mass: kg. SI unit of weight: N.
3) Mass does not change with location. Weight changes with location.
4) Spring balance is used to measure mass. Beam balance is used to measure weight.

Question 13

What are the five effects of forces on an object?

Answer 13

1) moves a stationary object
2) stops a moving object
3) changes the direction of motion of a moving object
4) change the shape and size of an object
5) causes an object to turn

Question 14

What are the two factors that affect the amount of pressure exerted?

You can also think about how to increase pressure exerted on an object.

Answer 14

1) force exerted
2) area of contact

It must be ‘area of contact’ and not just ‘area’ or ‘surface area’.

Increased force and smaller area of contact.

Question 15

What does it mean when we say ‘energy is conserved’?

Answer 15

Energy is not created or destroyed.
It is transferred from one object to another or converted from one form to another.

Question 16

What is the SI unit for energy?

Answer 16

joule (J)

Question 17

State the 7 sources of energy.

Answer 17

1) fossil fuels
2) solar energy
3) hydroeelctric energy
4) wind energy
5) geotherma energy
6) biofuel
7) nuclear energy

Question 18

State the impact of using fossil fuel on the environment.

impact can be good or bad.

Answer 18

1) release air pollutants and greenhouse gas
2) greenhouse gas contributes to global warming and causes climate changes

Question 19

State the impact of using solar energy on the environment.

impact can be good or bad.

Answer 19

1) generate electricity without producing pollutants and greenhouse gas.
2) Toxic wastes are produced during the production and disposal of solar panels.

Question 20

State the impact of using hydroelectric energy on the environment.

impact can be good or bad.

Answer 20

1) produces very little pollutants and greenhouse gas
2) causes flooding in the area behind a dam

Question 21

State the impact of using wind energy on the environment.

impact can be good or bad.

Answer 21

1) Does not produce pollutants or greenhouse gas.
2) destroy wildlife as large plots of land needed to be cleared.
3) Birds may be killed if they collided into the blades of the wind turbines.
4) Noise pollution for the nearby communities.

Question 22

State the impact of using geothermal energy on the environment.

impact can be good or bad.

Answer 22

1) Does not produce pollutants or greenhouse gas.
2) destroy wildlife as large plots of land needed to be cleared.
3) Toxic elements underground causes harm to environment if not handled properly.

Question 23

State the impact of using biofuel on the environment.

impact can be good or bad.

Answer 23

1) release air pollutants and greenhouse gas
2) greenhouse gas contributes to global warming and causes climate changes
3) Helps to recycle and reduces wastes as biofuels can be made from food wastes and used cooking oil.
4) Helps to reduce carbon dioxide in the air as plants are grown to produce biofuels.

Question 24

State the impact of using nuclear energy on the environment.

impact can be good or bad.

Answer 24

1) Does not produce pollutants or greenhouse gas.
2) Requires less and to build than a solar or wind farm.
3) Needed a lot of effort to research for ways to dispose and store nuclear wastes safely.

Question 25

What is the energy change in a fossil fuel power plant?

Answer 25

chemical energy -> heat energy -> kinetic energy (turbine) -> electrical energy (generator)

Question 26

What is the energy change in a hydroelectric power plant?

Answer 26

gravitational potential energy (water behind the dam) -> kinetic energy (water) -> kinetic energy (turbine) -> electrical energy (generator)

Question 27

What is the energy change in a wind power plant?

Answer 27

kinetic energy (wind) -> kinetic energy (turbine) -> electrical energy (generator)

Question 28

What is the energy change in a geothermal power plant?

Answer 28

heat energy (earth’s core) -> kinetic energy (steam) -> kinetic energy (turbine) -> electrical energy (generator)

Question 29

What is the energy change in a nuclear power plant?

Answer 29

nuclear energy (atoms) -> heat energy -> kinetic energy (turbine) -> electrical energy (generator)

Question 30

What is the energy change in a solar power plant?

Answer 30

light energy (sun)-> electrical energy (solar cell)

Question 31

What is the formula for pressure?

It is the relationship between pressure, force and contact area.

Answer 31

area refers to contact area

Question 32

What is the SI unit for pressure?

Recall the formula for pressure and the SI units used for each quantity.

Answer 32

N/m²
pascal (Pa)

Question 33

Explain why a knife must be sharp to cut things easily.

Think pressure and explain.

Answer 33

A sharp knife has a small contact area
which increases the pressure exerted on the things to be cut as pressure = force / contact area.
This allows things to be cut easily.

The same explanation can be used to explain why needles must be sharp.

Question 34

How is the pressure in liquid changes the deeper you are underwater?

Answer 34

The deeper we go underwater, the higher the pressure exerted.

Question 35

Explain why a dam’s wall needs to be thicker at the base than at the top.

Think pressure in liquid and explain.

Answer 35

The pressure of water at the base of the dam is higher than its top.
A thicker wall can withstand the high pressure better.

The same explanation can also be used to explain why the submarine needs a strong body to dive deep underwater.

Question 36

What is atmoshperic pressure?

Answer 36

It is the force exerted on a surface by the air above it.

Question 37

How does atmospheric pressure change as we climb up a mountain?

Answer 37

Atmospheric pressure decreases the higher we climb the mountain.

The higher we are at a mountain, the lesser the amount of air above us and thus lesser atmospheric pressure.

Question 38

How does a straw works to send liquid from the cup to our mouth?

Answer 38

When we suck on a straw, air is removed creating a lower than atmospheric pressure.
The higher atmospheric pressure pushes the liquid up through the straw allowing liquid to transfer from the cup to the mouth.