Newton's second law of motion

Question 1

True or false, any object accelerates when acted by a push or pull

Answer 1

true

Question 2

What is a net force

Answer 2

a combination of forces that act on an object

Question 3

True or false, acceleration is not dependent on net force

Answer 3

false

acceleration is dependent on net force

Question 4

true or false: acceleration is directly proportional to the net force

Answer 4

true

acceleration ~ net force; or use the fish symbol like in engsci

Question 5

what does directly proportional to mean?

Answer 5

that means the change in one is the same amount of change in the other

Question 6

When does friction occur?

Answer 6

when surfaces slide or tend to slide over one another, a force of friction acts

Question 7

What does friction do to the acceleration and net force of an object when a force is applied to the object?

Answer 7

friction:

• usually reduces the net force
• reduces the acceleration (usually)

Question 8

What causes friction?

Answer 8

the irregularities in the surface of mutual contact, and depends on the kinds of material and how much they are pressed together

Question 9

Where is the direction of friction force?

Answer 9

always in the direction of opposing motion

eg. an object sliding DOWN an incline experiences friction directed UP the incline

Question 10

Does zero net force result in zero acceleration?

Answer 10

yes

Question 11

true or false: no friction exists on a crate that sits at rest on a level floor

Answer 11

true

Question 12

You push on a crate that sits on a smooth floor and it accelerates. If you apply four times the net force, how much greater will be the acceleration?

Answer 12

4X greater

this is because acceleration ~ net force

Question 13

If you push with the same increased force on the same crate, but on a very rough floor, how will the acceleration compare to pushing on a smooth floor

Answer 13

it will have less acceleration because friction will reduce acceleration

Question 14

Why is it important not to JAM the breaks to make the tires stop?

Answer 14

It is very important that you not jam on the brakes so as to make the tires lock in place. When tires lock, they slide, providing less friction than if they are made to roll to stop.
While the tire is rolling, its surface does not slide along the road surface, and friction is static friction - and therefore greater than sliding friction

Question 15

What does the force of friction not dependent on?

Answer 15

speed

area of contact

Question 16

What do you collectively call liquids and gases?

Answer 16

fluids

Question 17

What do you call fluid friction?

Answer 17

drag

Question 18

true or false: drag in a fluid depends on the nature of the fluid

Answer 18

true

Question 19

true or false drag is greater in water than it is in air

Answer 19

true

Question 20

does drag depend on speed and area of contact?

Answer 20

yes it does, unlike friction

Question 21

True or false: for slow motion through water, drag is approximately proportional to the speed of the object

Answer 21

water drag ~ speed of object

true

Question 22

True or false: in air, drag at most speeds is proportional to the square of the speed

Answer 22

true

eg. if an airplane doubles it speed, it encounters 4X the drag
- at very high speed however the simple rules break down when the fluid flow becomes erratic

Question 23

What net force does a sliding crate experience when you exert a force of 110 N and friction between the crate and the floor is 100N?

Answer 23

10N in the direction of your push

Question 24

A jumbo jet cruises at constant velocity of 1000 km/h when the thrusting force of its engines is a constant 100 000N. What is the acceleration of the jet? What is the force of air resistance on the jet?

Answer 24

The acceleration is 0 because the velocity is constant. Since the acceleration is zero, it follows from Newton’s second law…