PHYS 101 Lecture Notes - Lecture 21: Free Body Diagram, Net Force

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byzantiumhorse747

23 Mar 2017

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Chapter 4: why things move as they do. There is a force exerted by the table on the block. This for(cid:272)e, (cid:449)hi(cid:272)h is perpe(cid:374)di(cid:272)ular to (cid:894)or (cid:862)(cid:374)or(cid:373)al(cid:863) to(cid:895) the surfa(cid:272)e of the table, pushes up on the block. The magnitude of the normal force is equal to the weight. To visualize the normal force, imagine that the table top is covered with springs: When an object, say a book, rests on the table, it squeezes the springs causing the springs to push back against the book. When an object is not accelerating (i. e. , whenever the velocity is constant), the sum of the forces must be zero. We dra(cid:449) the (cid:862)free (cid:271)od(cid:455) diagra(cid:373)(cid:863) (cid:894)a. k. a. a for(cid:272)e diagra(cid:373)(cid:895): Sum of forces = (normal force) + (weight) = 0. The net force on the block is 0. 0 = fnet = m a => a = 0. We ha(cid:448)e see(cid:374) the first t(cid:449)o of ne(cid:449)to(cid:374)"s la(cid:449)s of (cid:373)otio(cid:374):

Related Questions

A) A siring is tied to a book and pulled lightly as shown at right. The book remains in contact with the table and does not move. Draw a free-body diagram for the book. Label each of the forces exerted on the book as you were instructed in the tutorial Forces.

B) How do the forces exerted on the book, in this case, compare to the forces exerted on the book when the string is not present? List any forces that are the same (i.e., same type of force, same direction, and same magnitude) in both cases. Make a separate list of forces that change (or are not present) when the string is pulled.

C) Consider the following statement made by a student about a book at rest on a level table: "The two forces exerted on the book are the normal force directed up and the weight of the book directed down. These are equal and opposite to one another. By Newtons third law they are (action-reaction) force pair, so the normal force is always equal to the weight of the book." Do you agree with the student? Explain why you agree or disagree.

D) Consider a book on top of a level table while the book is being pressed straight down by a hand. In the space below, draw a free-body diagram for the book. Label the forces as you did in the tutorial Forces. How do the forces exerted on the book in this case compare to the forces exerted on the book when the hand is not pushing? List any forces that are the same (i.e., same type of force, same direction, and same magnitude) in both cases. Make a separate list of forces that change (or are not present) when the hand is pressing down on the book.

E) When the hand is pushing down on the book, is the magnitude of the weight equal to the magnitude of the normal force exerted by the table on the book? How can you tell?

byzantiumwhale17

Two dimensional dynamics often involves solving for two unknown quantities in two separate equations describing the total force. The block in (Figure 1) has a mass m=10kg and is being pulled by a force F on a table with coefficient of static friction

. Four forces act on it:

. The applied force FF (directed

above the horizontal).

. The force of gravity

(directly down, where

. The normal force N (directly up).

. The force of static friction fs (directly left, opposing any potential motion).

If we want to find the size of the necessary to just barely overcome static friction (in which case

, we use the condition that the sum of the forces in both directions must be 0. Using some basic trigonometry, we can write this condition out for the forces in both the horizontal and vertical directions, respectively, as:

In order to find the magnitude of force F, we have to solve a system of two equations with both F and the normal force NN unknown. Use the methods we have learned to find an expression for F in terms of

pucetiger860

a.) A hockey puck is observed to be sliding along a flatfrictionless surface at a speed of 4 cm/min. There is no net forceacting on the puck. Assuming it doesn't smash into anything, howfast will the puck be going 17 min later?
cm/min

b.) An object is accelerating. Which one of the followingstatements is true?
The object must be speeding up.
Gravity must be causing the object to accelerate.
The object must be changing directions.
The object must be slowing down.
There is a net force acting on the object.

c.) A 100 kg block weighs 220 lb on Earth. If the block weretransported to a planetary body that had a smaller free fallacceleration (as compared to Earth), which one of the followingwould be true?
The block would have the same weight and a smaller mass.
The block would have the same mass and a bigger weight.
The block would have the same mass and the same weight.
The block would have the same weight and a bigger mass.
The block would have the same mass and a smaller weight.
d.) What does it mean (in physics) to say that a quantity isconserved?
It means that the quantity is not being used.
It means the total amount is zero.
It means the total amount never changes.
It means it's being saved up.

e.) At a certain point in time, the total energy of a closed systemis observed to be 176 J. Which one of the following statements istrue?
Three hours later the energy of the system is 352 J.
Four hours later the energy of the system is 88 J.
All of the energy must be kinetic if the objects are moving.
Twelve hours later the energy of the system is 176 J.
Some of the energy must be potential.

g.) Which of the following statements are impossible? Choose allthat apply.
The parked truck had 8770 J of KE.
The scooter had 0 J of KE and 0 kgÂ·m/s of momentum.
A ball moving in a circle had 0 N of net force acting on it.
A box had an acceleration of 0 m/s2 while a net force of 311 Nacted on it.
Jack exerted 18 N of force due east on a cart. As a direct result,the cart exerted 18 N of force due west upon Jack.
A toothpick exerts a smaller gravitational force upon the Moon thanthe Moon exerts upon it.

a.) Two balls make up a closed system. Ball A has 701 J of energyand ball B has 78 J. After they collide, ball A has 665 J. How muchenergy does ball B have after they collide?
J

b.) An asteroid and a comet collide head on. Prior to thecollision, the asteroid has a momentum of 700,000 kgÂ·m/s up and thecomet has a momentum of 800,000 kgÂ·m/s down. After the collisionthe asteroid has a momentum of 750,000 kgÂ·m/s down. After thecollision, what is the comet's momentum?
kgÂ·m/s
North
South
East
West
Up
Down
Left
Right
No direction because the comet has stopped

c.) How much does a 28 kg object weigh on Moon? Please feel free toreference the Solar System Data table located at the beginning ofUnit II.
______N

d.) A 660 N net force acts on a 42 kg object. Determine theobject's acceleration.
_____m/s2

e.) Calculate the gravitational force between a 657 kg object(resting on Earth) and the Moon. The mass of the Moon is 7.347Ã1022kg and the distance between the object & the Moon is 3.844Ã108m.
____N

PHYS 101 Lecture Notes - Lecture 21: Free Body Diagram, Net Force

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