GE EDITORS: Alec Rodriguez, Kyle McKenney, Chloe Suridis, David Jelke, and Scott Renshaw

Natland Note: (11/08/13)

  • Some notes are missing and/or a bit hard to read
  • some of the multi-body system notes and pulley notes are cut off otr blurry.
  • Make sure to post solutions to the "sample problems" that you posted below
    • It is hard to read several of sample problems below.
  • Make sure to post pictures from the internet and cite where you got them below.
  • Be sure to include the pages and numbers for the conceptual questions, Ranking Tasks, etc. discussed in class (and examples that we mention)
  • Here is an important file to post (after the relevant, prior class notes). This is the file with the methods to calculate the normal force. Make sure to embed this as a picture document in the appropriate place below - not as a document as I have it here
  • Here is a nice computer program/game that addresses acceleration and velocity of a Martian or Lunar lander! You can embed this simulation on your page the same way that I embedded the projectile motion simulator on the "kinematics" wiki. Let me know if you have questions about how to do this. Someone needs to do this.

Make sure ALL of you are posting on the website if you ALL want full credit for the LAB GRADE!

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external image ferrari-f2008-launch-6.jpg
external image ferrari-f2008-launch-6.jpg

-The wing on the front of the car adds a greater force downward which, in turn, increases the normal force. Since the normal force is increased, the maximum static frictional force increases, which makes the car less likely to skid and thus it can take turns at faster speeds (and it can accelerate faster).

external image thirdLawPairs.png
The free body diagram above showcases forces such as the normal force (FN) and the tension force (FT).

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This free body diagram shows two masses, one which is hanging and the other which is on an incline, attached to each other via a rope on a pulley system. Note how the tension force will be the same for both objects (because they are attached the to the same rope; tension is equal throughout the rope) and how the coordinate system is aligned with the incline.

photo 4_2_2_2.JPG<---- Ths
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Free-Body Diagram examples from class (Thursday 10/10 and Friday 10/11)

Ex 1) A mass held by a string

Ex 2) Mass hanging from 2 strings

Ex 3) Mass hanging from 2 strings, off-center

Ex 4) Mass hanging from 2 stings attached to a hanger (hint: they are all one system)
So in this FBD the reason there are two forces of static friction going upward is because Natland was holding the system with two fingers, so therefore, there needs to be a force of static friction between each finger and the system.

Ex 5) Eraser held against a wall
In this FBD, the fs1 is the force of static friction between Natland's finger and the erase and the fs2 is the force of static friction between the eraser and the wall.

Ex 6) Eraser held at an upward angle against a frictionless wall
Here, Fay and Fax are the components of the applied force, Fa

Ex 7) Box rests against 2 perpendicular surfaces

Ex 8) Pushing against a chair, but it does not move
The reason there is a force of static friction to the left is because the only way the chair would not move is due to static friction between it and the ground.

The following images are Mr. Natland's normal force examples sheet that is available as a link to download on the top of the page.
Natland normal force pics 2.jpg
Natland Pics 1.jpg

Multi-Body Systems


Atwood's Machine Notes (Working with two objects separately or as a system)

Atwood's 1.jpg

Atwood's 2.jpg

Uniform Circular Motion (UCM)

8 Examples of UCM




Here's a video of a guy standing in a gravitron. The reason he can stand up is due to his inertia and the force of static friction between his shoes and the wall. His inertia keeps him there because his tendency is to stay in the current state of motion so he will continuously want to go in a straight line but the walls keep him going in a circle, so the result is he is pressed into the wall.


This is a video of what happens when a car goes around a curve and exceeds the maximum velocity possible before skidding out. This is why static friction is so important for driving and centripetal motion.


Space Station Images and Clips
external image Spacestation70s84201310.jpg
Artist's conception as to what a space station with simulated gravity could look like...What would it be like to be standing on the "ground" above? Note the orientation of the people and the housing!

external image 2013-08-09-elysium_external_space_station-533x219.jpg
Image of the space station from the movie "Elysium" (2013).

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Another image of the space station from the movie "Elysium" (2013). It appears there is nothing "closing in" the area where people live to "hold in" the atmosphere....could this be possible? (2:19 - but start watching the video at 0:54)
(This is a clip of Stanley Kubric's "2001: A Space Odyssey" showing what it would be like to run in a rotating section of a spaceship, simulating gravity) (4:47)
(This shows a clip from Kubric's "2001: A Space Odyssey" showing the rotating space station from the outside)

Loop-de-Loop problem
external image rcd.gif
external image rcd.gif

- In a roller coaster, what keeps the car moving along the curved path is the centripetal force. The centripetal force prevents the car from exiting the curve by continuously making it change its direction toward the center of the circle. In this example, for the most part the centripetal force is the normal force. Gravity also pulls down on the car with a constant force, whether it moves uphill, downhill, or through the loop. At the very bottom of the loop, gravity and the centripetal force act in different directions. On the other hand, at the very top of the loop, both the normal force and the force of gravity act in the same direction to produce the centripetal force. No matter what, the centripetal force always points towards the center of the circle.

Note: If you are asked how fast the car may be going just before losing contact with the tracks, then the normal force between the car and tracks is zero.


Class "Warm up" conceptual Questions:
Newtonian Forces:
  • pg 92 #2, 3
  • pg 93 #5
  • pg 95 #6
  • pg 99 #7, 8, 9, 10
  • pg 103 figure 4.19
  • pg 109 #14, 15, 17
  • pg 115 #20
  • pg 125 #3, 9, 11, 13
  • pg 126 #16
  • Ranking task pages: 15, 24, 26, 28, 29, 35, 36, 38, 39

Circular Motion:
  • pg 139 #1-5
  • pg 143 #6-9
  • pg 147 #11
  • pg 148 Figure 5.19
  • pg 151 #12 and Figure 5.21
  • pg 152 #13, 14
  • pg 155 #7, 8, 11, 15

Extra Sample Problems:

Practice Problem 1 (PP1):
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  • PP1 Solution:

PP2, PP3, & PP4:
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  • PP2, PP3, & PP4 Solutions:

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  • PP5 Solution:
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  • PP6 Solution:

PP7 & PP8:
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  • PP7 & PP8 Solutions:

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Conceptual questions for Uniform Circular Motion:
1) The speedometer of your car shows that you are traveling at a speed of 35 m/s. Is it possible that your car is accelerating?
2) Consider two people, one on the earth's surface at the equator and the other at the north pole. Which has the larger centripetal acceleration?
3) Which of the following statements about centripetal acceleration is true?
a. an object moving at a constant velocity cannot have a centripetal acceleration.
b. an object moving at a constant speed may have a centripetal acceleration.
4) Other things being equal, would it be easier to drive at high speed around an unbanked horizontal curve on the moon that to drive around the same curve on the earth?
5) What is the chance of a light car safely rounding an unbaked curve on an icy road as compared to that of a heavy car: worse, the same, or better? Assume that both cars have the same speed and are equipped with identical tires.
6) A penny is placed on a rotating turntable. Where on the turntable does the penny require the largest centripetal force to remain in place, at the center of the turntable or at the edge of the turntable?
7) Two satellites are placed in orbit, one about Mars and the other about Jupiter, such that the orbital speeds are the same. Mars has the smaller mass. Is the radius of the satellite in orbit about Mars less that, greater than, or equal to the radius of the satellite orbiting Jupiter?
8) The acceleration due to gravity on the moon is 1/6 that on earth. a) Is the true weight of a person on the moon less than, greater than, or equal to the true weight of the same person on the earth? b) is the apparent weight of a person in orbit about the moon less than, greater than, or equal to the apparent weight of the same person in orbit about the earth?
9) Would a change in the earth's mass affect a) the banking of airplanes as they turn, b) the banking of roadbeds, c) the speeds with which satellites are put into circular orbits, and d) the performance of the loop-the-loop motorcycle stunt?
10) A stone is ties to a string and whirled around in a circle at a constant speed. Is the string more likely to break when the circle is horizontal or when it is vertical? Assume the constant speed is the same in each case.

1) Yes, if you're going around a curve. You are constantly changing direction.
2) The person at the equator. The person on the north pole is on the axis of rotation and therefore has 0 centripetal acceleration.
3) a and b
4) No
5) The same. Mass cancels out in the equation because of the inertial factor. The only thing that matters is the coefficient of static friction between the tire and road. Being that the tires are identical the chance remains the same.
6) Edge of the turntable. If it were in the center of the turntable, there would be a centripetal acceleration of 0 because that would be the axis of rotation.
7) Less than. the formula used for this problem is F(gravity) = (mv^2)/r -> [Gm(obj)m(planet)]/r^2 = [M(obj)v^2]/r
8)a. less than, b. equal to
9) Yes for all four
10) vertical because mg is acting in the opposite direction of the string.

For a beautifully drawn video doodle of the hammer problem from Ch. 5 #59, check out this link.

WEBSITES: (0:41)
(Fun video of famous physics professor, Paul Hewitt, showing a classic demonstration of inertia!) (1:08)
("BMW Motorcycles S1000RR Stunt"...a fun trick to demonstrate inertia....but it is REALLY a trick! To see why, go to next video!)

Balloon video (5:16)
(This is Mythbusters testing out the above example. Do you think they "called it right" by making the objects less massive at the end? Do you think the mass of all the objects on the table makes a difference such that making it lighter would be helpful?) (1:12)
("7 inertia demos") (23:52)
("Understanding Car Crashes: When Physics Meets Biology." This video, sponsored by the Insurance Institute of Highway Safety, goes into how and why the body sustains injuries during car crashes. This video goes into a field of applied physics called "Injury Biomechanics" at the Institute's giant research center.)
("Video talking about the force of gravity in the Assassin's creed video game")

Conceptual question: Movie Physics Edition Note anything you see in the following two videos that are consistent with Newton's laws, and then note anything you see that seems to violate any of them.
Part I:

Part 2:

Image result for rocket launch
Image result for rocket launch

Space Shuttle Launch Compilation

Rocket Launch Compilation (3:42)
("Inside the Gravitron". Video is long, but just flip through portions of it to see what it is like...around 2:55 for example)
ride the gravitron like a boss.jpgriding-the-gravitron-like-a-boss-big.jpg
The Round-Up Carnival Ride

(/Aboard NASA's// '//Vomit Comet//' - RIT students experience zero gravity while conducting reduced-gravity scientific experiments aboard NASA's "Vomit Comet" aircraft; reported by Kelly Downs of RIT University News.)
(Hypoxia - 4 of spades)
(An accurate, not-so-useful comic discussing the centripetal vs. centrifugal force)
(An article about the 5 points of Lagrange, where gravitation forces balance so something placed at one of these points will remain there - useful for potentially building a space station?)
external image 250px-Lagrange_points_Earth_vs_Moon.jpg
external image 250px-Lagrange_points_Earth_vs_Moon.jpg

The above diagram shows the five Lagrangian points in a two-body system with one body far more massive than the other (e.g. the Earth and the Moon). In such a system L3-L5 will appear to share the secondary's orbit, although in fact they are situated slightly outside it. An object placed in orbit around L5 (or L4) will remain there indefinitely without having to expend fuel to keep its position, whereas an object placed at L1, L2 or L3 (all points of unstable equilibrium) may have to expend fuel if it drifts off the point.
(How Stuff Works article about space stations)
(information about the international space station)
jsc2012e219094 -- The International Space Station
jsc2012e219094 -- The International Space Station
external image InternationalSpaceStation.jpg
Image above shows the comparative size of the international space station to a football field. The living quarters are

Facts about the Space Station:
Orbital Height: 230 mi
Max Speed: 17,200 mph
Module Length: 51 m (1:00)
(5 Motorcycle Circus Ball....Circular Motion!) (3:18)
("Wringing out Water on the ISS - for science!) (2:54)
("Karen Nyberg Shows How You Wash Hair in Space") (4:57)
("Gravity Opening Scene" (0:57)
("Slinky Drop" - Veritasium) (3:31)
("Slinky Drop Answer" - Veritasium) (1:57)
("Slinky Drop Extended" - Veritasium) (3:33)
("G-Monster to 9G's)

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external image Alexander_Gerst_ready_for_a_centrifuge_training_session.jpg
("Centrifuge Training")
("9G Centrifuge Training")
"Apollo Ohno Takes 1000 m gold"
"Steven Bradbury | Salt Lake 2002 Winter Olympics"

How a clothes dryer works
Artwork showing the sequence of steps involved in drying clothes with an electric clothes drying machine.
Artwork showing the sequence of steps involved in drying clothes with an electric clothes drying machine.

Importance of balancing a centrifuge....
What causes the seasons?
Image result
Image result

Earth's tilt is the reason for the seasons. View of Earth in relation to sun during each of the four seasons. The hemisphere receiving the direct rays of the sun has summer while the hemisphere tilted away from the sun, thus getting its rays from more of an angle, has winter.
Earth's tilt is the reason for the seasons. View of Earth in relation to sun during each of the four seasons. The hemisphere receiving the direct rays of the sun has summer while the hemisphere tilted away from the sun, thus getting its rays from more of an angle, has winter.

What Causes the tides?
An animation of Tides

Animation of lunar day
Animation of lunar day

Unlike a 24-hour solar day, a lunar day lasts 24 hours and 50 minutes. This occurs because the moon revolves around the Earth in the same direction that the Earth is rotating on its axis. Therefore, it takes the Earth an extra 50 minutes to “catch up” to the moon. Since the Earth rotates through two tidal “bulges” every lunar day, we experience two high and two low tides every 24 hours and 50 minutes. Here, we see the relationship between the tidal cycle and the lunar day. High tides occur 12 hours and 25 minutes apart, taking six hours and 12.5 minutes for the water at the shore to go from high to low, and then from low to high.

Animation of spring and neap tides
Animation of spring and neap tides

Together, the gravitational pull of the moon and the sun affect the Earth’s tides on a monthly basis. When the sun, moon, and Earth are in alignment (at the time of the new or full moon), the solar tide has an additive effect on the lunar tide, creating extra-high high tides, and very low, low tides — both commonly called spring tides. One week later, when the sun and moon are at right angles to each other, the solar tide partially cancels out the lunar tide and produces moderate tides known as neap tides. During each lunar month, two sets of spring and two sets of neap tides occur (Sumich, J.L., 1996).


Union of Concerned Scientists (USA)
Article about the movie "Elysium" from a blog on the Scientific American. I got some of the screenshots from the movie from this article.
(This is where the animation for the "loop-de-loop" came from)
This is where the FBD picture (of the figure dragging the box) came from.
This is where the second FBD picture came from.

Additions to the Forces Wiki:


Graph Questions:
(Skip last two on impulse)

Concepts of Tug of War:

Arnie and Wimpy are playing tug-of-war. Arnie wins, pulling Wimpy into the mud puddle. Why did Arnie win?
a) Arnie exerted a greater horizontal component of force on the rope than Wimpy exerted.
b) The rope exerted a greater horizontal component of force on Wimpy than it exerted on Arnie.
c) Arnie exerted a greater horizontal component of force on the ground than Wimpy exerted.
d) All of the above.
Answer: At the start everyone is at rest. For someone to win, there must be an acceleration from rest to initiate motion in one direction. This acceleration need not be large. During the acceleration there must be a net horizontal force component on each person in the direction of the acceleration.

(a) and (b) are wrong because the rope has relatively small mass, so the tension forces at its ends are nearly the same size (F =ma where m is essentially zero). Certainly any small difference in tension between the two ends is nowhere near great enough to account for the outcome. The rope's mass is very small compared to the masses of Arnie and Wimpy, so even when it accelerates (and so do they), the net force on the rope, F = ma, is negligibly small compared to the net forces on Arnie and Wimpy. In fact, most of this game involves small accelerations.

(c) is correct. The net horizontal force component on Arnie that allows him to accelerate with respect to the ground is the force of the ground on his feet minus the force the rope exerts on him, the former being larger. The person with the better shoes, greater coefficient of friction at the ground underfoot, and foot control, wins. Wimpy also accelerates, because the force of the rope on him is larger than the force of the ground on his feet. The player wins who can maintain the largest horizontal force between his feet and the ground.
(d) is the response most students choose.

Website with practice questions and scenarios: