FORCE, MOTION, AND GRAVITATION

Question 1

what is mass

Answer 1

measure of the

• amount of matter in the object
• a numerical measure of its inertia

Question 2

what is the symbol for mass

Answer 2

m

Question 3

what is the measure for m

Answer 3

kilograms (kg)

Question 4

does mass change

Answer 4

the same on earth and in space

Question 5

what is weight

Answer 5

the force of gravity on the object

Question 6

how is weight calculated

Answer 6

(w = mg)
weight = mass x acceleration of gravity

Question 7

what is the unit for weight

Answer 7

Newton (N)

Question 8

what is the gravity at the surface of the earth

Answer 8

9.8m/s2

Question 9

What is the force acting on an object in free fall (within earth)?

Answer 9

Gravity

Question 10

Where does the expression of weight for an object in free fall come from?

Answer 10

From Newton’s second law

Question 11

What is the centre of mass

Answer 11

point where all of the mass of an object is concentrated.

Question 12

What happens to an object supported at the centre of its mass?

Answer 12

it will remain in static equilibrium

Question 13

What is Newton’s first law termed as

Answer 13

Law of inertia

Question 14

What does Newton’s first law/law of inertia state

Answer 14

Object in a state of motion or a state of rest will remain in that state unless a net force acts upon it.

Question 15

By what law do passengers inside a bus fall backwards when a bus moves from standstill

Answer 15

Due to inertia of rest

Question 16

Why do passengers actually fall backwards when a bus moves

Answer 16

Lower part of passenger body moves along with bus.

Upper part of the body retain state of rest (inertia).

Consequently, the passenger will fall backward.

Question 17

What is Newton’s second law

Answer 17

When object acted upon by net force MEANS

object’s state of motion =
•inversely proportional to the mass (m) of the object.
•directly proportional to the net force (F) acting upon the object.

Question 18

What is the formula for Newton’s second law

Answer 18

Force = Mass x Acceleration

Question 19

What is Newton’s third law

Answer 19

For every action, there is an equal and opposite reaction

Question 20

Contextualise Newton’s third law to an example of object A and object B

Answer 20

This means that when object A applies a force to object B, object A will experience a force of equal magnitude to object B but in the opposite direction.

Question 21

Contextualise Newton’s third law to the motion of an eagle flying

Answer 21

Eagle’s wings push air downwards

Air must also push eagle upwards.

Size of force on the air = size of force on the eagle.

The direction of the force on the air (downwards) is opposite the direction of the force on the eagle (upwards).

Question 22

Explain the action-reaction property details of Newton’s third law

Answer 22

For every action, there is an equal (in size) and opposite (in direction) reaction.

Question 23

Contextualise Newton’s Third law using a hammer and nail example

Answer 23

When hitting a nail with a hammer, the force of the nail on the hammer is equal to the force of the hammer on the nail.

Forces act in the opposite direction of each other.

Question 24

What is the simple rule of the gravitation law

Answer 24

there is a force of attraction existing between any two bodies of masses in the universe

Question 25

What is the detailed gravitation law

Answer 25

force is proportional to both of the masses m1 and m2

force is inversely proportional to the square of the distance, r, between their centre of mass.

Question 26

how is r measured for the gravitation law

Answer 26

From the centre of mass of one object to the next object (not from surfaces)

Question 27

what is the gravitation law formula

Answer 27

F = G (m1,m2/r2)

F = G x (m1 x m2)
—————
r^2

Question 28

What value is G for Newton’s universal law of gravitation

Answer 28

G = 6.673 x 10-^11 m3 kg-1 s-2.

Question 29

One Newton of force is enough to do what?

Answer 29

one N is the force needed to accelerate one kg of mass at the rate of one m/s2.

Question 30

What does Newton’s gravitation law provide

Answer 30

This formula gives the magnitude of the force without direction.

Question 31

How do you determine the centre of mass of a pole

Answer 31

An easy way to determine the location of the centre of mass of a rigid pole is to support the pole horizontally on one finger from each hand.

Gently slide your fingers together. When your fingers meet, you will be at the centre of mass at which time you can easily hold up the pole with only one finger as long as it can withstand the entire weight of the pole.

Question 32

If an object is uniform/regular, where is the centre of mass

Answer 32

If the object is uniform, a meter stick for example, the centre of mass will be at the exact geometric centre;

Question 33

If an object is irregular, where is the centre of mass concentrated

Answer 33

if the object is irregular in shape, such as a hammer, the centre of mass will be closer to the heavier end.

Question 34

Of any object, what kind of property is the centre of gravity

Answer 34

Centre of gravity is a geometric property of any object.

The centre of gravity is also the average location of the weight of an object.

Question 35

The motion of any object in space can be described in terms of centres of gravity, how

Answer 35

It is

• translation of the centre of gravity of the object from one place to another
• rotation of the object about its centre of gravity if it is free to rotate.

Question 36

What is free fall motion

Answer 36

vertical motion of an object with reference towards earth.