thomma+ch4

'Maurel Thom's Wikilog - Period 6 CP Physics - Burns - 2011

Chapter 4

SECTION 3
What Do You See? A frog is springing off a table and the height is being recorded.

What Do You Think?

=
A roller coaster makes its way up a hill with the help of electronic tracks. It would probably cost more to run a car with more people on it because the weight would be increased, which would require more energy.======

Physics Talk SPE - Spring Potential Energy - the energy stored in a spring when it is stretched out or compressed (similar to EPE). GPE increases the higher an object and as it moves down, GPE decreases and KE increases. SPE= 1/2kx^2 GPE, KE, and SPE always have the same sum (remain constant).

Checking Up 1. After a spring is released, the SPE gradually transforms in GPE after an object gains altitude. GPE is max at the top and SPE is 0. 2. Right after the spring is released, the KE will be 2Joules because the spring energy has been transferred to kinetic energy. 3. Since SPE and GPE are constant, the GPE at the top will be the same as the SPE at the bottom. 4. Spring potential energy is determined by the spring constant and how much the spring is compressed.

Physics to Go 5. There would be more GPE at the top of the second hill if it is bigger than the first hill. 6. Without friction, the cart would never stop and continue to go over each hill and never slow down. 7. GPE = mgh 300*15*9. 8= 44100J 8. KE = 1/2mv^2 (200)(15)^2 = 45,000J b) GPE = 45,000 when KE is 0 c) GPE = mgh 45,000=400*9.8*h h=11.5m 9. GPE = mgh, so as height increases, GPE does as well. 10. All three will be the same because they all finish in the same place. Length of the paths have no effect. 11. Yes, GPE =.0784J KE = .0724J b) SPE = GPE SPE = .0784J  c) height = .13m 12. GPE = KE 52,920J = 1/2kx^2 52,920 = 1/2K*(4^2) 52,920 = 1/2k*16 k = 6,615 b) 70560 = 1/2(6615)(x^2) x = 4.62m  13. SPE = KE  1/2k*x^2 = KE  1.8J = KE

What Do You Think Now? A roller coaster cart is pulled up by a chain. The energy that the cart has at the top of the hill must remain the same throughout the ride in order for it to function. That way, the cart can go through all the loops and hills without stopping.

SECTION 4
What Do You See There is a roller coaster on the moon and a roller coaster on Jupiter. Jupiter's roller coaster is more fun because there is more gravity.

What Do You Think Gravity's direction is toward the center of the planet. People in Australia are held on Earth the same way everybody else is. They are being pulled towards the center of the Earth's core.

Physics Talk - Gravitational Field: the gravitational influence in the space around a massive object - Inverse-square relationship describes the relationship between the magnitude of a gravitational force and the distance from the mass it is. - Newtons Law of Universal Gravity - Every point of mass in the universe is attracted to every other point of mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them (Fg=G*m1*m2/r^2) r is the distance between their centers m1 and m2 are the masses of the bodies G is the universal constant (6.67*10^-11N) - Gravity is the force of attraction between two bodies according to their masses. - Kepler’s First Law: The planets travel in an ellipses around the Sun. An ellipse is a mathematical shape that is defined by two foci (an oval). The Sun is at one focus. There is nothing at the other focus. - Kepler’s Second law: The planets sweep out equal areas in equal times. Imagine a pizza in the shape of an ellipse. Slices of pizza are cut from one of the foci. Each slice of pizza has the same area. The planets would travel along the edge of the ellipse. The time needed to travel along the edge of each slice of pizza would be identical. Since the edge of the pizza represents the path of the planet around the Sun, this means that the planet travels faster when it is near the Sun and slower when it is further from the Sun.where T is the time to complete one orbit and R is the average distance from the Sun. - Kepler’s Third law: There is a mathematical relationship that defines the time it takes for a planet to complete an orbit about the Sun and the average distance of the planet from the Sun. - The [Henry] Cavendish experiment was a test where Cavendish used a few several KG masses and used a tiny twist of quartz fiber to suspend them. This proved that Gravity was universal.

Checking Up 1. In the classroom, gravity's direction is downwards towards the center of the Earth, as it is anywhere else in the world. 2. The gravitational field is strongest where the field lines are closest, or closer to the object. 3. The force of gravity would be 1/9th as large. 4. Earths gravitational pull makes the moon orbit. 5. Elliptical, or an ellipses.

Physics to Go 1. force =125N

2. 1/4 as great b) 1/9th as great c) 1/16th as great

3. Gravity keeps people on the ground, and the planets and moons in orbit. Without Earths gravitational pull, we would float away and the moon would go off in a tangent or hurtling towards a planet or star.

4. The gravity would be greater at the top of the ride because it is closer to the center mass meaning that there will be a smaller denomenator meaning a grater force.

5. The water is closer to the moon than to the earths core b) The moons pull causes the water to push and pull on the earth. c) There is more water on the sides because the moon orbitals horizontally, so it pulls the sides more than the top or bottom.

6. If there wasn't gravity to keep the fish or the water in place, the whole ecosystem would be drastically altered. b) Gravity holds the fish and the water down or else both would fall of the Earth.

7. 1/4th as much b) 1/9th as much c) 1/16th as much d. 4x as much

8. force = 2x b) force = 3x c) force = 4x d) force = 1/2

9. force = 4x b) force = 9x c) force = 16x d) force = 1/6th

10. force = 2x b) force = 9x c.) force = 6x

Physics Plus 1. A = v^2/r 2. v = d/t (2)(3.14)(3.84*10^8)/2440800 v = 998.5m/s 3. A = v^2/r a = 998.5m/s^2/3.84*10^8\ a = .0025m/s^2

What Do You Think Now? Gravity's direction is towards the center of the Earth, that is why people in Australia don't fall off the Earth's surface and water stays in the ocean. The Earth's mass is so great, that it creates its own gravitational pull.

Section 5 What Do You See? Two delis using two different scales to measure meat.

What Do You Think? No, you can't use the same scale for a canary and an elephant. The weight of an elephant is much larger than that of a canary, so the scale that would be needed to weight an elephant would not be precise enough to weigh a canary.

A bathroom scale measures the force of gravity that you are exerting on it.

Physics to Go 1. 100*9.8 = 980N b) 10*9.8 = 98N c) 60*9.8 = 588N

2. 520N b) 4,000N c) 200N

3c The slope is y=14.91 N/m k d)

Section 6

What Do You See A hefty man is standing on a scale on a downward moving elevator, but the scale reads "O".

What Do You Think Your mass never changes, but your weight would change on a roller coaster. Weight is relevant to a downward force, therefore, on a roller coaster, your weight would be less as you were going down a drop. If you were sitting on a bathroom scale, the reading would go up right as you accelerated upwards, and down as you were thrown down the hills.

Physics Talk Newton's First Law - an object at rest stays at rest, an object in motion stays in motion, unless acted on by an unbalanced force Newton's Second Law - unbalanced force. creates an acceleration (the bigger force is in the same direction as acceleration [use motion map and draw FBD]). Net Force = Mass(acceleration) incr. right = T > f incr. left = f > T decr. right = f > T decr. left = T > f

Physics to Go

Section 6, PTG #4

1. Vi=0, Vf=Vi+at Vf = 0+at a) Vf = 9.8(2) 19.6m/s  b) Vf=9.8(5) = 49m/s c) Vf = 9.8(10) = 98m/s

2. V f= Vi+at Vi = 0 a) Vf = 1.6(2) =3.2m/s  b) Vf=1.6(5) = 8m/s c) Vf =1.6 (10) = 16m/s Acceleration and ∑ are always the same.
 * **Motion of the Elevator** || **Acceleration (up, down, zero)** ||  || **Relative Scale Reading (greater, less or equal to weight)** ||
 * At rest, bottom floor || zero ||  || equal N=W ||
 * Starting at Rest, Increasing Up || up ||  || greater N>W ||
 * Continuing to move, Constant Up || zero ||  || equal N=W ||
 * Slowing down to top floor, Decreasing Up || up ||  || less NW ||

5. Since the apparent weight appears smaller than the actual weight, the motion is must either be deceasing up or increasing down because acceleration is negative, or down.

6. If the person were standing on a bathroom scale in an elevator, the weight reading would also go up. The person would feel heavier. The normal force on the scale would be bigger than the weight. Velocity (Up). Acceleration (Up).

7. Once the elevator descends, the scale reading will be lighter. W > N. b) F = ma F=50*1.5= 75N  490-Fscale=75  =415

8. 50 kg w = m(g) = 50(9.8) = 490 N b) N - mg = ma =50(2) + 490 N = 590N c) Since there is no acceleration, it would read 490. 9. In the first sketch, the elevator is either at rest or moving in a constant speed with no acceleration. b. in the second sketch, acceleration is down, meaning that the weight is greater than the normal force so the apparent weight is less c. In the third sketch, the elevator is accelerating up, so the Normal force will be greater than the weight meaning that the apparent weight is greater

Checking Up 1. The sum of all the forces would be zero. 2. The reading would be greater, net force would be up. 3. When you accelerate upward, you feel heavier because the normal force would be greater than you weight. 4. You're not exerting a force, so the scale would read zero. 5. Air resistance. Section 6, PTG #4

What Do You Think Now No your actual weight never actually changes, it is your apparent weight that changes. Acceleration and ∑ (net force) are always in the same direction, but when acceleration and velocity are opposite, you feel a shift in weight. If you were sitting on a scale, you would feel lighter in the middle of a drop at heavier at the bottom of a drop. Throughout a loop, you would have to feel heavier all the time, or else you wouldn't be able to make it through the loop.

Section 7

What Do You See A fast moving cart on a roller coaster is about to fall off on a curve.

What Do You Think During a loop, you have enough speed and momentum to carry you over the top.

Physics Talk Centripetal force is any of the main forces (normal, tension, weight, or friction) that points to the center of a circle Centripetal force always points towards the center of a circle, regardless of position

Checking Up 1. Centripetal force. 2. You have to accelerate or else you won't keep moving. 3. Normal and weight. 4. Direct relationship. Inverse on the radius. Directed Squared Relationship. 5. Larger when speed is increases, larger when mass increases, larger when the radius decreases.

Physics to Go 1. The car would travel in a circle b) The car would travel in a straight line, or tangent to the circle 2. Friction makes you move in a circle. If the car were to hit a patch of ice, it would move straight, or tangent to the circle 6. Speed did not change. Velocity did. Velocity includes direction and it changed from East to North. 7. 20^2/200 = 2

10. Fast-moving roller coaster At the top of the loop: Normal Force = 3500 N At the bottom of the loop: Force of Gravity = 500 N Normal Force = 6500 N

Slow-moving roller coaster At the top of the loop: Weight = 500 N. Normal Force = 300 N At the bottom of the loop: Weight = 500 N. Normal Force = 3,300 N

13. Bottom of the Hill - Normal b) Top of Vertical Loop - Heavy c) Bottom of Vertical Loop - Heavy d) Bottom of the Hill - Normal e) Lift - Normal

14. Bottom of the Hill - Zero b) Top of Vertical Loop - Down c) Bottom of Vertical Loop - Up d) Bottom of Hill(2) - Zero e) Constant Lift hill - Zero f) Horizontal Loop - Sideways, proportional to the loop g) Back Curve - Sideways, proportional to the curve

Physics Plus 1. The net force (∑F ) increases because they are directly proportional b) If the force speed of the object moving around the circle increases, the force required to keep it moving in a circle also increases.\ 2. The track most be as strong as the square of the speed. 3. If the radius increases, then the new force decreases. 4. The larger the radius for the curve, the smaller the force required to keep the car moving along the curve. If the curve is tight (r is very small) then a greater force is required. 5. As the radius gets bigger, the force gets smaller. Once the radius is, the force required is also zero (because that's what you're dividing by).

What Do You Think Now? You don't fall out of a loop because of the centripetal force. Your net force is always pointing towards the center of the loop.

Section 8

What Do You See A team of people are exerting themselves to pull a roller coaster up to the top of an incline, but once they reach the top, it takes no effort for them to get back down.

What Do You Think It takes the same amount of energy because GPE will be the same - its based on height. A steeper incline means the force of gravity feels stronger because you're doing more work in a shorter amount of time or distance.

Physics Talk Watt: the unit of measurement for Power. (W) 1 W = 1 J/s Power: has fast work is done and energy is transferred - work done during an elapsed amount of time. (w/t). ho P= (work done)/(time elapsed) Work: amount of energy used over a certain distance. Work = force (parallel to the displacement) x displacement W = Fxd

Checking Up 1. Gravitational Potential Energy is at the top. 2. Work due to GPE of cart at top of loop. 3. Power decreases over time. 4. Energy transfers to Work or GPE. 5. Watt.

Physics To Go 1. The GPE at the top of the incline would be mass x gravity x the height of the cart, which would be greater than at the bottom of the incline, which would be zero. b) All of the work is done by gravity, but the energy transferred to KE as it began to move. c) The amount of work done by the spring would have to be equal to the carts total energy. d) 1/2kx^2 e) There is a little GPE, but mostly KE. f) The cart begins to slow down when the spring begins to compress.

2. Work is zero because the force and distance are not in the same direction b) W = F xD = 60(.5) W=30N c) W = F x D = 75(40) W = 3,000 d) W = F x D = 500(.7) = 350 N

3. Instead of conserve energy, transfer energy, because the energy will always move from one force to another while remaining the same 4. If clay were used, then the mass would increase, causing GPE and KE to also increase. 5. W = FxD = 10,000(20) W = 200,000N b) P = (work)/(time) = 200,000/150 = 1,333 J/s 6. As the roller coaster goes up the very first hill, GPE increases. At the top, GPE is at its highest point for the ride, and the energy transfer to KE as the roller coaster goes down the first hill. KE and GPE are exchanged as the roller coaster goes up and down hills (GPE>KE the higher up, GPE<KE the lower down). At the end, work is done by the brakes to slow the coaster, and eventually come to a stop.

What Do You Think Now Yes it does take more energy to get a roller coaster up a steeper incline because more work force needs to be done. The amount of force that has to be done in the same amount of distance would have to be greater to get up a steeper incline.

Section 9

What Do You See Two students are trying to decide whether to use energy or force to calculate some measurements for a roller coaster. The student using energy is having a much easier time than the student using force, who is stuck,

What Do You Think Even though the speed may be the same throughout the ride, sudden changes in direction might cause you to feel heavier or lighter, which causes a thrill.

Physics Talk Force always has direction Distance, speed, and energy are scalar quantities Energy concepts - heights and velocities. All energies can be calculated, and they are measured in joules. Force and energy are related.

Physics To Go 1. a^2+b^2 = c^2 25+25= 50 square root 50 = 7 b) change in velocity = 2.1m/s @ 45 degrees

2. The speeds will be the same because both tracks have the same GPE because they both have the same initial height. 3. distance - scalar b) displacement - vector c) speed - scalar d) velocity - vector e) acceleration f) force - vector g) KE - scalar h) PR - scalar i) work - vector

4. 30km - scalar b) 600N - vector c) KE 1200J - Vector d) 30m/s - Vector

5. It's best to use energy when dealing with GPE, like when trying to figure out the amount of energy it takes to get up the first hill of a rollar coaster. It's better to use force when using a straight track or a circle.

Checking Up 1. Pythagorean Theroum is needed to add vector quantities. 2. Energy = Scaler Force=Vector 3. GPE, KE, and the total energy. 4. The energy doesn't depend on the path the coaster takes. 5. Work done is required.

What Do You Think Now Inclines with changing direction add to the thrill of a ride.

Section 10

What Do You See The roller coaster is very unsafe. People are parachuting off and carts are flying off the track. Peoples faces are flying back, which probably means that the force of gravity is too great.

What Do You Think Yes it does, Some people might want to go on a roller coaster more if they think they might get hurt - those people are thrill-seekers. Other people are more concerned about their safety and might avoid the ride. Yes, if a significant number of people die, then the amount of people who would want to ride that ride would significantly reduce, or go to 0 altogether.

Physics Talk Acceleration - safe values --> up to 4 G's Ac= V^2/R If values are greater than 4 G's: - radius increase - lower velocity; reduce height of start, increase height of position When a car is moving in a circle, centripetal force is required. Centripetal acceleration must be towards the center of the circle. Free fall provides an acceleration of 1 G.

Checking Up 1. 4 G's. 2. Decrease the initial height or increase the height of a turn. 3. At the bottom, there is the most KE. 4. The bottom

Physics to Go

2. 9.8h=200 = 20m b) a= 400/12 = 33 m/s^2 c) No d) 22 m/s e) 17 m/s

3. a = 25^2/10 = 63 m/s^2 b) Yes

4. 9.8(50) = 1/2V^2 = 31 m/s b) a = 961/10 = 96 m/s^2 c) 588 = v^2 = 24 m/s^2 d) 58 m/s^2 e) Yes. There are less than 4 G's.

5. 8.9 m/s b) 20m

6. 8.0 m/s b) 7,200N c) track on wheels

7. 26.7 m/s^2 b) 24,000N

Physics Plus 1. GPE = KE 9.8h = 450 = 45.9m b) A = v^2 r A = 100 c) force is over 4 G's = not safe d) 39.2 = v^2/r 352.8 = v^2 18.8m/s^2 = v e) 39.2 m/s^2 =v^2/r 274.4 = v^2 16.6 m/s = v f) GPE = KE 273.42 = 1/2v^2 23.4 = v g) a = v^2/r A = 60.2 = 6 G's = unsafe h) N+W = MAc v^2/9 = 9.8 v = 9.4

2. w = mg = 9,800 N=9,800N 3. N>9,800N N>9,8000N N<9,8000N

4. Fc=mv^2/r Fc = 18,800N 5. Fc = mv^2/r = 18,800N 6.18,800N b) W = mg = 9800N c) N-w = mv^2/r N = 28,600N

What Do You Think Now If the ride is not properly designed, the bottom of the track before going into a loop, and the top of the loop would be the most dangerous. Those are the areas where the roller coaster is most thrilling and need the most track strength. Also, if the roller coaster does not have enough speed at the top of the loop, then the car would fall out. In addition, you don't want your riders blacking out from a significant amount of exposure to G's (over 4 G's).

Section 11

What Do You See An instrument is being made. A string is attached to a weight, and a cup is being used to amplify the sound. The weight creates tension, so the string will vibrate and give off a sound.

What Do You Think Guitarists and violinists make different sound by adjusting the position of their finger on the string. The closer to the to the fret holes the finger are, the higher the note. On a guitar, to make the highest pitch note, you would theoretically put your hand on the lowest string (in relation to the ground) and closest to the sound hole.

Chapter 5
frequency = #waves/sec = Hertz period = #sec/1 wave wave speed = v = (lambda)f f = frequency T = tension m = mass of string L = length of string