Physics Review - Newton's Laws and Forces

7 months ago

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

7 months ago

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.

7 months ago

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.

7 months ago
AnimeLuver10023:

Is there suppose to be a question here?

7 months ago

@Vocaloid

6 months ago

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?

6 months ago

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?

6 months ago
Vocaloid:

second scenario looks good too

6 months ago
Vocaloid:

what exactly do you mean by inverse relationship?

6 months ago
Vocaloid:

are you talking about a = F/m?

6 months ago

Yes

6 months ago
Vocaloid:

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"?

6 months ago
Vocaloid:

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

6 months ago
Vocaloid:

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

6 months ago

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?

6 months ago
Vocaloid:

yes

6 months ago

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?

6 months ago
Vocaloid:

yup, that's the jist of it

6 months ago

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.

6 months ago
Vocaloid:

good ^^

6 months ago

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.

6 months ago
Vocaloid:

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

6 months ago
Vocaloid:

9.8 m/s^2 to be precise

6 months ago

Okay, I forgot that

6 months ago

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

6 months ago
Vocaloid:

well done

6 months ago

Have to remember the units for Newtons as well $\frac{ kg \times m }{ s^2 }$

6 months ago

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?

6 months ago

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

6 months ago
Vocaloid:

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

6 months ago

Mhm true

6 months ago

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

6 months ago

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

6 months ago
Vocaloid:

good, well done

6 months ago

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

6 months ago

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).

6 months ago
Vocaloid:

good

6 months ago

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

6 months ago

10. What are some examples of objects that are not in equilibrium? A person being jostled in a crowd.

6 months ago

11. What are some examples of field forces? Magnetism and gravity

6 months ago

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,

6 months ago
Vocaloid:

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

6 months ago

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"

6 months ago
Vocaloid:

yeah those are good answers ^^

6 months ago

Time for the fun ones to begin

6 months ago

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.

6 months ago

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.

6 months ago

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

6 months ago
Vocaloid:

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

6 months ago
Vocaloid:

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

6 months ago
Vocaloid:

direction of force + acceleration are both forward?

6 months ago