Question

Physics Review - Newton's Laws and Forces

Answer 1

Goals:

Know Newton's Laws and how to apply them
Memorize the vocabulary
Be able to solve all the problems on the study guide without staring into space

Answer 2

Vocabulary:

Force - a push or a pull on an object

Contact Force - a force that requires physical contact between objects

Field Force - a force that does not require physical contact to act

Inertia - the tendency of an object to maintain it's state of motion

Mass - the measure of the quantity of inertia (measured in kilograms)

Weight - the force due to gravity acting on an object

Normal Force - the force a surface exerts on an object
*Normal means perpendicular so the normal force always acts perpendicular to the surface.

Tension - the pulling force in a rope or string

Equilibrium - when the net force on an object is zero

Static Equilibrium - when an object is not moving

Dynamic Equilibrium - when an object is moving at a constant velocity (no acceleration)

Net force - the total amount of force acting on an object or the sum of all the forces acting on an object

Free-body diagram - a picture showing all forces acting on an object using arrows to represent the forces.

Answer 3

1. State Newton's Laws of Motion

First Law - an object will maintain it's state of motion either at rest or moving with a constant velocity unless acted upon by an unbalanced external force.

Second Law - the acceleration of an object is directly proportional to the net force on the object and inversely proportional to the objects mass.

Third Law - If object A exerts a force on object B, object B exerts a force on object A that is equal in magnitude but in the opposite direction.

*The forces act on different objects
*Forces always come in pairs

Action-reaction pair- a pair of forces that exemplifies Newton's Third Law.

Answer 4

Is there suppose to be a question here?

Answer 5

@Vocaloid

Answer 6

2. A crate accelerates across the floor with an acceleration, a. If you double the force applied to the crate, what would be the new acceleration? What if you doubled the force and cut the mass in half?

Answer 7

For this one, I would say the acceleration doubles in the first instance, and then quadruples in the second instance.

This is due to Newton's Second Law, where force is directly proportional to acceleration and inversely proportional to mass. Therefore if force doubles, acceleration doubles.

Though how would you describe the inverse relationship?

Answer 8

second scenario looks good too

Answer 9

what exactly do you mean by inverse relationship?

Answer 10

are you talking about a = F/m?

Answer 11

Yes

Answer 12

something like "acceleration is directly proportional to force and inversely proportional to mass, since acceleration on an object increases w/ force and decreases w/ mass, linearly"?

Answer 13

as for the reason, "objects with more mass have more inertia which means they will accelerate less under the same force"

Answer 14

I'm not 100% sure what you're looking for here;;

Answer 15

So a simple approach to describing the relationship between mass and acceleration is that whatever happens to one, the inverse operation happens to the other?

Answer 16

yes

Answer 17

3. What is inertia?

You kind of already described this one. But as far as my understanding goes...

Inertia is the tendency of an object to stay at rest/in motion. Mass, as you said, directly ties into this. Objects with low mass have low inertia, and objects with high mass have high inertia.

This one is kind of easy to conceptualize, as what is more difficult to stop when its coming down a hill...a large boulder, or a cute pebble?

Answer 18

yup, that's the jist of it

Answer 19

4. Which has more inertia, a bowling ball or a basketball?

Bowling balls are not meant to be stopped, therefore they have high mass in order to discourage diversion in their course. Thus they have more inertia than a basketball which must have lower mass in order to be more easily used by basketball players.

Answer 20

good ^^

Answer 21

5. Your new motorcycle has a mass of 250 kg. What is its weight?

I know that mass is not a measure of weight, so I would say something along those lines, and then that weight is not given.

Answer 22

you can convert from mass to weight by multiplying mass by the earth's gravitational constant 9.8

Answer 23

9.8 m/s^2 to be precise

Answer 24

Okay, I forgot that

Answer 25

\[250 kg \times \frac{ 9.8m }{ s^2 }= 2450 N\]

Answer 26

well done

Answer 27

Have to remember the units for Newtons as well

\[\frac{ kg \times m }{ s^2 }\]

Answer 28

6. A rock has a mass of 3.0 kg on Earth. If you took the rock with you deep into outer space where the rock is weightless, what would be the rock's mass?

Answer 29

Since there are no forces to hinder the rock, shouldn't it be able to just fly with impunity?

Answer 30

well, yeah, if a force were applied to it then it would keep flying with no air resistance

but the question is simply asking about its mass, which is constant no matter what the location is

Answer 31

Mhm true

Answer 32

7. A car of mass 1000 kg accelerates at 1.5m/s^2. Determine the net force acting on the car.

Answer 33

\[F = ma\]
\[F = (1000 kg)(\frac{ 1.5m }{ s^2 })\]
\[F = 1500 N\]

Answer 34

good, well done

Answer 35

8. What are some examples of objects in a state of dynamic equilibrium ?

Answer 36

Boring example: A car maintaining a speed of 35m/hr

Fun one: A ballistic projectile fired in space by a railgun maintains its velocity until it hits an opposing ship (First Law).

Answer 37

good

Answer 38

9. What are some examples of objects in a state of static equilibrium?

My pencil when I do not know the answer to a physics question.

This one is fine.. xD

Answer 39

10. What are some examples of objects that are not in equilibrium?

A person being jostled in a crowd.

Answer 40

11. What are some examples of field forces?

Magnetism and gravity

Answer 41

12. What are some examples of contact forces?

Pulling on a book to remove it from a shelf. or pushing a cart through the aisles of Walmart,

Answer 42

for contact forces they (might) be looking for specific types like "normal force" and "friction force"

Answer 43

Hmm yes.

"Placing an banana on table, then the table exerts normal force on an object to support it"

"Rubbing two sticks together to generate a campfire, with friction being the present contact force"

Answer 44

yeah those are good answers ^^

Answer 45

Time for the fun ones to begin

Answer 46

13. When you press on the accelerator in your car, how do you feel? What is the direction of the force on your body (forward or backward) ? What is the direction of the acceleration of your body? Explain why you feel the way you do.

Answer 47

When you press on the accelerator the car surges forward. However, as per Newton's First Law of Motion, you do not. You maintain your state of motion (at rest), but the car moves forward causing you to be pushed against the car seat.

Do not know hows to describe the force and acceleration though.

Answer 48

I suppose the feeling would be "being pushed up against the seat" or "falling backwards."

Answer 49

I've been looking on the web for a concise explanation for this and if I understand correctly : the apparent force is caused by the difference in your velocity relative to the car's velocity. the seat exerts a normal force in the opposite direction of the motion

Answer 50

every source just talks about inertia w/o describing the actual forces rip

Answer 51

direction of force + acceleration are both forward?

Answer 52

I know that relative to the car, you always have a velocity of zero.

I checked the back answer and it has Fnet and acceleration as forward. Force and acceleration as always being in the same direction. So since both are forward, I can see that normal force would be what opposes that.

Answer 53

makes sense ^^

thankfully 14 and 15 are more straightforward