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PENN STATE / Physics / PHYS 211 / What is contact force?

What is contact force?

What is contact force?


School: Pennsylvania State University
Department: Physics
Course: General Physics:Mechanics
Term: Fall 2015
Tags: Physics, 211, Physics211, exam, Exam 2, practice problems, practice, practice exams, and practice finals
Cost: 50
Name: PHYS 211 Exam 2 Study Guide and Practice Problems
Description: This study guide covers all of Exam 2 material and goes over a lot of practice problems that will be extremely helpful for the exam.
Uploaded: 03/09/2018
11 Pages 21 Views 20 Unlocks

PHYS 211 Midterm Study Guide  

What is contact force?

Study guide is most useful with my notes that give highly important diagrams I will also skip useless and unimportant subchapters so you save a lot of time studying from my study guide. This study guide highlights only the important parts of my notes, so you save time​. ____________________________________________________________________________

Equations to know how to use​ (a lot, but most are similar and easy to understand): 1. Fnet = ma

2. Fg = mg

3. Fg = (GmM)/r2 

4. Fs = usn

What is a long-range force?

5. Fk = ukn

6. Fr = urn

7. Fd = -½CpAv2 

8. ac = v2/r = w2r

9. T = 2pi/w = 2pi*r/v = 1/f We also discuss several other topics like kensha clark

10. Fs = Static Friction

11. Fk = Kinetic Friction

12. Fr = Rolling Friction

13. Fg = Force of Gravity If you want to learn more check out pols2401

G = 6.67x10-11 Nm2/kg2 

What is a mass?

Fd = Drag Force

T = Tension Force

Ft = Thrust Force

ac = Centripetal acceleration (acceleration towards the center)

T = Period

w = Angular velocity

v = Linear Velocity

r = Radius

f = Frequency

Know unit circle (easy points on easy questions) 


Chapter 5 – Force and Motion ​(mostly definitions and explanation, not important chapter) 5.1-Force: 

Force- Acts on an object

Agent- Something that exerts a force

Contact Force- Two objects touching

Long Range Force- Forces acting on each other without physical contact Force Examples: Don't forget about the age old question of example of cultural particulars


1. Force parallel to surface

2. If it keeps object stationary = static friction (Fs)

3. If it opposes motion = kinetic friction (Fk)

5.5-Newton’s Second Law: 

Fnet = ma We also discuss several other topics like materiality constraint

m = mass

a = acceleration

5.6-Newton’s First Law: 

Law of inertia: 

1. Object at rest, stays at rest unless acted upon by an outside Force

2. Object in motion, stays in motion unless acted upon by an outside Force

*Objects accelerations do not change unless a new force is added

If Fnet = 0 that object has:

● Constant velocity

○ That object’s velocity could be +, -, or 0

● Acceleration = 0

Inertial Reference Frame- When Fnet = 0 an object is an inertial reference frame, because it is not accelerating

____________________________________________________________________________ Chapter 6 – Motion Along a Line Don't forget about the age old question of emily indriolo

6.1-Equilibrium Model: 

Objects with a net force of 0 (Fnet = 0) have NO acceleration

Objects in Equilibrium Examples: 

6.2-Using Newton’s Second Law: We also discuss several other topics like imotu

The forces acting on an object determine its acceleration

Fnet = ma 

We can use this and our past knowledge from other chapters to solve for Vffrom Vi and Fnet Examples ​(next page):

6.3- Mass, Weight, and Gravity: 

Mass is unchanging (mass = how much “stuff is in an object”)

An object’s weight depends upon the gravity of where it is (less on the moon than on Earth) Gravity- Long range attractive force between two objects (Fg = (GmM)/r2) m = mass of smaller object

M = mass of larger object

*Gravity gets weaker as distance increases

Gravity on an object on Earth = FEarth = mg (straight down)

*Something will weigh more while accelerating up (in an elevator), but mass will stay the same


Static Friction: 

1. Force on an object that keeps it from moving

2. Matches a force trying to move an object, until it is overcome

6.5 Drag ​(not important subchapter, but just know what the formula means): Drag Coefficient- Tells how strong of a force is going against motion

Fd = -½CpAv2in the direction opposite of motion

A = Area of object

p = density of air (1.3 kg/m3 at 0oC)

C = Drag coefficient (smaller for more aerodynamic objects

____________________________________________________________________________ Chapter 7 – Newton’s Third Law 

7.1-Interacting Objects: 

Any time an object, A, pushed or pulls on another object, B, then that object, B, pushes or pulls back on A

Every force is part of an action reaction pair: 

-Earth pulls down on you

-You pull up on the Earth

Example​ (next page):

*When walking, what force makes you move forward?

Ans:​ The Earth pushing forward against you (because you push back on it) 7.3-Newton’s Third Law: 

As stated before objects A and B exert a force on each other

-The Force of A on B is equal to Force B on A

-These two Forces are in opposite directions

Ex​ (stated before): 

The Earth pulls down on you, and you pull up on the Earth with equal Force Thought Question: 

A car is pushing a truck. The mass of the truck is much larger than the mass of the car. What can be said about the forces between the two?

Ans:​ The car exerts the same amount of force on the truck as the truck exerts on the truck - Equal Force and opposite direction

7.4-Ropes and Pulleys​ (many practice problems): 

Tension Forces- in ropes is causing by the stretching of their “spring-like molecular bonds” -Don’t remember that...it’s useless

-Just know Tension is a force applied by a rope or pulley!!!

Practice Problems​ (next page and answers follow picture or are in picture):

Ans:​ Less than (rope 1 has to pull the weight of A and B, whereas 2 only pulls the weight of B)

Ans:​ Equal to (both ropes experience a force of tension equal to mg)

____________________________________________________________________________ Chapter 8 – Dynamic II: Motion in a Plane: 

8.1-Dynamics in Two Dimensions: 

Linear motion and Two-Dimensional motion follow the same rules of Fnet = ma Example of Two Dimensions: 

A Rocket Launching upwards with wind pushing it. How far does the wind push it? Rocket Mass = 30 kg

Thrust Force = 1500 N

Wind Force = 20 N

Distance up = 1,000 m

How will this Force affect the object’s momentum: 

Ans:​ It slows down, and curves downward

8.2-Uniform Circular Motion: 

ac = v2/r = w2r 

That is an old equation, but now we have to know how forces cause this acceleration Therefore we can say:

Fnet = mac = mv2/r = = mw2r 

Example of Formula Use​ (picture on next page): 

Question: A father puts his 20 kg child in a 5 kg cart, and swings him with a 2 meter rope creating a tension of 100 N. What is the RPM of the cart?

What is the maximum speed a 1,500 kg car can make a left turn around a curve of 50 m without sliding? (Static friction coefficient is 1)

A highway curve of radius 70 m is banked at an angle of 15 degrees. At what speed can a car take this bank without assistance from friction?

A Stone Age hunter swings a 1 kg rock around his head with a 1 m rope. If the rope breaks at a Tension of 200 N, what is the max angular speed, in rpm, he can swing the rock?

8.5-Nonuniform Circular Motion: 

Objects are in Nonuniform Circular Motion when they are following a circular path, and its speed is changing

- Along with centripetal acceleration, there is tangential acceleration

-Remember v is positive when counterclockwise and negative when clockwise -Force follows the same rules 

A 1,500 kg car is going around a 25 m radius track, starting from rest. The wheels supply a constant 525 N Force in the forward direction. The coefficient of static friction between the tires and road is 0.9. How many revolutions have been made when the car slides off the track?

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