Chapter 9: Interactions

Question 1

what does W stand for?

Answer 1

• weight/ gravitational force acting on an object

Question 2

what does G stand for?

Answer 2

gravitational field strength acting on the object

Question 3

what does M stand for?

Answer 3

Mass of an object

Question 4

How do you find Weight?

Answer 4

w = mg
- ( triangle w at the top and at the bottom is m and g )

Question 5

what is pressure and its si unit

Answer 5

Pressure is the force exerted on an unit area
Pa

Question 6

what are contact and non contact forces

Answer 6

contact forces- friction and elastic force
non-contact- gravitational and magnetic force

Question 7

how do you find pressure?

Answer 7

Pressure = Force divided by Contact Area
- ( for triangle force is on top while p and c is at the bottom )

Question 8

when does pressure increase?

Answer 8

• when the contact area is smaller
• when contact area is larger, there is less pressure exerted
• When there is more force applied

Question 9

what is the si unit for force?

Answer 9

N

Question 10

Why would someone be more likely to get hurt if they step on a nail, but be completely fine if they lie on a bed of nails?

Answer 10

The bed of nails have a significantly larger area of contact. The same force ( the person’s height ) will produce a much lower pressure if she lies on the bed, reducing injury.

• ( basically the larger the contact area, the more pressure produced )

Question 11

is force and mass related?

Answer 11

No!! Thus if force is reduced, mass will not be affected.

Question 12

What is a pivot?

Answer 12

It is the location/ point of contact.

• ( a turning effect MUST have a pivot. )

Question 13

Does the length of a lever ( something that helps to exert force ) affect the force needed to do something?

Answer 13

Yes!! The longer the lever is, the less force is needed.

Question 14

referring to page 13,
Explain how the application of a force can help one to remove the lid of the tin can easily.

Answer 14

• When the screwdriver is wedged between the tin can and the lid, it acts as a lever.
• When the screwdriver is pushed down, the downwards force creates a turning effect about the pivot
• This results in an upwards force applied on the lid, prying the lid open.

keywords: lever, downwards force creates a turning effect about the pivot, upwards force is applied

Question 15

If there were 4 people and they were standing at various heights, in order, who would be experiencing the most pressure. ( 1 is the lowest 4 is the highest )

Answer 15

1 - most pressure
2
3
4 - least amount of pressure.

1 experiences the most pressure due to them experiencing the most amount of air particles
note: air particles has mass

Question 16

Why are suction cups able to stick onto the wall?

Answer 16

1. When a suction cup is suck onto the wall, air is pushed out from under the suction cup. The air pressure between the suction cup and the surface decreases. It becomes lower than the atmospheric pressure
2. The higher atmospheric pressure hold the suction cup in place.

Question 17

How do you find work done?

Answer 17

Force x distance moved in the same direction as the force

W at the top of the triangle then F | D

Question 18

Is there any work done if someone is carrying a box and held it in a fixed position?

Answer 18

There is no work done!! Although there is force applied to hold the box in a fixed position, the box did not move in the direction as the force!

Question 19

If a box is pushed and moves forward, would any work be done?

Answer 19

There is work done!! The force moved the box in the same direction as the force applied. Work is done to move the box forward.

Question 20

If a box is lifted vertically from the floor, would there be any work done?

Answer 20

There is work done!! An upwards force is applied to lift the box in the same direction as the force.
Work is done to lift the box up.

Question 21

If a box is carried and moved forwards, would there any work done in moving the box.

Answer 21

There is no work done!! The distance moved by the box was not in the same direction as the force applied to carry the box.

Question 22

If Tessa dashes horizontally 30 m, and her bag weighs 60 N, what is the work done by Tessa while carrying her school bag?

Answer 22

There is no work done as the force of her bag is in a downwards direction.
60 N x 0 = 0 J

Question 23

What is the Si unit for work done?

Answer 23

J for Joules!

Question 24

Alicia kicks a ball which weighs 50 N horizontally, with a force of 60 N across the field 200 m away from her. What is the force done by Alicia to the ball

Answer 24

60 N x 200 m = 12000 J !!

If you used 50 N, it’s incorrect because 50 N represents the downward/ gravitational force acting on the ball.

Question 25

If the tip of a pin is sharper, the force that the pins exerts on the wood will be higher.

True or False?

Answer 25

False!!
The force remains the same, pressure increases when the contact area is smaller.
basically force will not be affected but pressure will be.
cuz pin sharper less contact area yeah hahaha yeah :,)

Question 26

What happens when a boy sucks onto the straw

Answer 26

When the boy sucks onto the straw, some air is pushed out of the straw. The air pressure inside the bottle decreases and becomes lower than the surrounding atmospheric pressure

The higher atmospheric pressure pushes the liquid up the straw into the boy’s mouth.

Question 27

if the tip of the pin is sharper, the force the pin exerts on the wood will be higher. Is this true

Answer 27

No. Force remains the same, however the pressure increases when the contact area is smaller.

Question 28

What is work done on an object?

Answer 28

It is the transfer of energy when an object moves in the same direction as the force applied.

Question 29

What is friction and elastic force?

Answer 29

friction is a force that opposes motion between two surfaces in contact

elastic force is force acting on a stretched or compressed elastic object to return it to its original shape

Question 30

What is gravitational force, weight and magnetic force

Answer 30

Gravitational force is a force that attracts two objects towards each other
weight is gravitational force exerted on an object by a planet
magnetic force is a force exerted between a magnet and a magnetic material or between two magnets

Question 31

What are the factors affecting work done

Answer 31

• force applied
• distance moved by object in the direction force is applied.

Question 32

Why are the bases of dams thicker than the top?

Answer 32

Because water pressure is higher at the base of the dam, thus a thicker wall is better able to withstand the high pressure.