Chapter+4

=Chapter 4=

Section 5
What do you think?

Yes you can use the same scale to weight both an elephant and a canary, it would just have to have a very large surface area and be able to support the immense weight of the elephant, while easily handling the canary.

Bathroom scales measure the force of the gravitation pull on the masses that are on them. AKA tell you your weight.

Physics Talk

Checking Up

PTG

What do you think now?

It isn't realistic to weight a canary and an elephant on the same scale.A scale would have to be calibrated for very low weights in order to give an accurate reading for a canary. This same scale would break if an elephant were to be weighted on it. A scale that would be used to weight an elephant would be able to register very high weights but wouldn't recognize small weights such as the canary; it's weight simply wouldn't register on this larger scale.

Section 6
What do you think?

Physics Talk

Checking Up #1-5

PTG #1-6

PTG #4
 * **Motion of the Elevator** || **Acceleration (up, down, zero)** ||  || **Relative Scale Reading (greater, less or equal to weight)** ||
 * At rest, bottom floor || zero ||  || N = W ||
 * Starting at Rest, Increasing Up || up ||  || N < W ||
 * Continuing to move, Constant Up || zero ||  || N = W ||
 * Slowing down to top floor, Decreasing Up || down ||  || N > W ||
 * At rest, top floor || zero ||  || N = W ||
 * Starting at rest, Increasing Down || down ||  || N > W ||
 * Continuing to move, Constant Down || zero ||  || N = W ||
 * Coming to a stop on the ground floor || up ||  || N < W ||

Apparent Weight How your weight appears to change due to the affects of acceleration.

Free body Diagram: Normal pointing up and weight pointing down. Compare: Velocity/Acceleration/Sum of Forces

What do you think now?

Your weight only appears to change when you are on a roller coaster. When your speed increases upward your acceleration is in the same direction, since your acceleration is increasing you feel heavier. When your speed is decreasing your acceleration and velocity are in opposite directions. If you are decreasing upward, your acceleration is negative and you feel lighter. The opposites of these are true for downward motion. When you are moving at constant motion in any direction, there is no change in your acceleration and your weight remains the same.

Section 7
What Do You Think?

You are moving too fast and do not accelerate downwards fast enough to fall. Your centripetal force is towards the center of the loop and this makes you follow the trck.

Section 8
Section 8

What Do You Think?

If the hills are of equal heights than it does not matter how steep they are, it will take the same amount of energy. If one is taller than the other than that taller one will require more energy to summit.

It is more difficult to climb up a steep incline than a gentle incline because you're walking more against gravity and it is also harder to gain a good footing on the ground to effectively push off of.

Physics Talk Summary

The Physics Talk starts out by reviewing the concept of work and describes how the amount of work you need to lift a roller coaster up a certain hill is equal to the GPE it has at the summit of said hill. It then goes on to talk about how roller coaster cars are raised with electrical energy from motors. No matter what the system for getting the roller coaster up to a certain height the total energy between GPE and other factors will remain the same throughout all the steps from beginning to end. Afterwards it talks about how some energy is lost from KE in the form of heat and sound energy. As opposed to a situation where KE and GPE balance each other out alone. The last two sections talk about brakes and power. Brakes on the coaster convert KE to thermal energy and bring it to rest, there is also usually a back up system using springs to stop the roller coaster, this form of braking converts the KE to EPE. Power is a new concept introduced hear used to describe how quickly work is done. If you pull a cart either slowly or quickly up a ramp it will use the same amount of force to do the work, but the faster it is done the greater the power of the motion. It is defined as the work done divided by the time elapsed; the speed at which work is done and energy is transferred. It is measured in Watts (J/s).

Checking Up #1-5


 * 1) 1 The work done to get the cart to the summit is converted into GPE.


 * 1) 2 From the work of the motor pulling it up the hill.


 * 1) 3 Although the work required is the same the force required is actually much less because the work is divided up throughout a much larger distance. This is why it is easier to push a heavy object up an incline rather than lift it straight up.


 * 1) 4 When a roller coaster breaks KE is converted into Thermal Energy through friction.


 * 1) 5 Watts (J/s) are the unit of power.

What Do You Think Now?

The steepness of the incline does not affect the amount of energy needed to get it up, the height determines the amount of energy needed to get the mass to the top.

It is harder to walk up a steep incline than a gentle incline because it requires more power. Since a steeper incline is closer to going straight up it uses more work in a shorter amount of time.

Physics To Go #1-6

1. a) The GPE at the top of the cart is maximum amount of energy the system can have. The GPE at the bottom of the ramp is 0.

b) W = length of the ramp * weight of the cart

c) The same amount of energy that the cart had in GPE form at the top of the hill.

d) Equal to the amount of energy the cart had in GPE form at the top of the hill.

e) Also equal to the GPE at the summit.

f) As soon as it makes contact with the spring.

2. a) 0, the force is not perpendicular to the direction of movement.

b) W = F*d W = 60 * .5 W = 30 J

c) W = F*d W = 75 * 40 W = 3,000 J

d) W = F*d W = 500 * .7 W = 350 J

3. Minimize Energy Use

4. It would require more work to move the cart up the hill.

5. W = F*d W = 10,000 * 20 W = 200,000 J

P = W/t P = 200,000/150 P = 1333.3 J/s

6. Throughout the ride the initial GPE it starts with is converted into KE, the balance between these constantly changes throughout the ride and then at the end the remaining KE is turned into Thermal Energy from the friction of braking the coaster to rest.

Section 9
What Do You Think?

The most thrilling parts will be anytime it changes direction. When it turns you will be pushed into your seat and the closer the turns are grouped together the more you will be shaken around and this can cause excitement in a person and depending on the speed it can stimulate the secretion of adrenaline.