Ns-Term 3 - Unit 1: Forces pg 205-224

Question 1

what is a force?

Answer 1

it is a push or pull

Question 2

what unit is force measured in?

Answer 2

It is measured in newton (N)

Question 3

name 5 possible things that could happen if force is exerted on an object

Answer 3

• speeding up or slowing down
• deformation
• rotation
• direction can change
• object can come to a standstill

Question 4

how to forces always act?

Answer 4

forces always act in pairs

Question 5

Define force pairs

Answer 5

forces of equal magnitude which simultaneously work in opposite directions

Question 6

what are the two types of forces and explain what happens in them.

Answer 6

• non-contact or field forces
  • work over a distance (action-over-a-distance)
• contact forces
  • object touches another object

Question 7

give examples of non-contact/ field forces

Answer 7

1. gravitational forces
2. magnetic forces
3. electrostatic forces

Question 8

give examples of contact forces

Answer 8

1. mechanical forces
2. applied force
3. friction forces
4. normal force
5. tension force/tension
6. air resistance
7. elastic forces in springs

Question 10

What is gravitational force?

Answer 10

force with which the earth attracts objects

Question 11

give examples of of objects that attract each other

Answer 11

• the sun and planets
• earth and moon
• earth and objects on earths surface

Question 12

what direction is gravitational attractive force?

Answer 12

it is always towards the center of the object

Question 13

define mass

Answer 13

an indication of the amount of matter and is measured in kilograms

(the mass remains constant)

Question 14

define weight

Answer 14

attraction force that the earth (or a planet) exert on an object. It is measured in newton

(weight changes)

Question 15

do the masses and radii of planets differ?

Answer 15

yes, the masses and radii of planets differ; therefore the attractive force exert by each planet on objects differ

Question 16

write down the formula to calculate weight

Answer 16

Fg=w=mg

e.g.
An astronauts mass is 100kg. calculate his weight on earth and on the moon

Earth: Moon:
Fg=w=mg Fg=w=mg
= (100)(9,8). = (100)(1,6)
=980N =160N

Question 17

define magnetic forces

Answer 17

force with which magnetic substances attract or repel each other

Question 18

name the 3 metals that magnets attract

Answer 18

iron, nickel, cobalt

Question 19

what are materials that are attracted by magnets known as?

Answer 19

ferromagnetic substances

Question 20

what are the two types of electrical charge?

Answer 20

• positive charge

* negative charge

Question 21

what happens in a positive charge?

Answer 21

the object releases electrons

Question 22

what happens in a negative charge?

Answer 22

objects accept electrons

Question 23

what does an atom consist of?

Answer 23

•protons (+charge)
•neutrons (neutral charge)
(both in the nucleus)

•electrons (- charge)
(space around the nucleus)

Question 24

how is energy stored in cells?

Answer 24

It is stored in the form of potential energy

Question 25

explain how lighting is formed

Answer 25

• particles and droplets in clouds rub and bump against each other, and become charged
• big amounts of negative and positive charges are separated
• lot of the negative charges accumulate mainly in the bottom part of the cloud and positive charges in the top part
• these separated charges causes potential energy
• when discharged, it is converted into electrical energy and then converted into light and heat energy

Question 26

define electrostatic forces

Answer 26

forces exerted by charges objects

Question 27

Name 3 safety measures that can be taken during lightning

Answer 27

1. Avoid outdoor activities in bad weather
2. Rather don’t bath or shower
3. Avoid using telephones or electrical apparatus