Physics Test Chapter 8

Why does the sun wobble as it moves through space?

Because its orbiting planets cause a shift in the sun's center of mass

Why is centrifugal force considered a fictitious force?

Because the force has no agent such as mass and no interacting counterparts

Where is the center of gravity of a hammer located?

In the more massive end of the hammer --> near the head

How can you locate the center of gravity of an object?

1. By drawing lines straight down from suspension points 2. By looking at the intersecting lines drawn from suspension points 3. By balancing it above your finger

Give three examples of objects that have their center of gravity located at a point where there is no mass?

1. donut 2. basketball 3. boomerang

Give four examples of units of rotational speed?

1. revolutions per second 2. rotations per second 3. revolutions per minute 4. rotations per minute

A rock polisher with a radius of 30.0 cm turns with a frequency of 0.35 Hz. What is the centripetal acceleration of a small rock wedged on the inside wall of the tumbler?

1.4 m/s^2

People in the future live inside a rotating space structure that is 4 km in diameter. Inside the structure, people on the inside of the outer edge will experience 3 g while people halfway to the axis will experience how much gravity?

1.5 g

What is centrifugal force?

an outward force that can attribute to circular motion

Define Centripetal Force.

any force that causes an object to follow a circular path

An object will always stop with its center of gravity where?

as low as possible

Why does a person weigh slightly less at the equator than at the poles?

because the tangential speed of the earth is greater at the equator, people are essentially pushed off the scales

Why does a tennis ball whirled on the end of a string move in a circle?

because there is an inward force acting on the ball

The long heavy tail of a squirrel enables it to easily vary what?

its center of gravity

In which direction on Earth should you travel in order to decrease your weight when you live in the Northern Hemisphere? Why?

south→ go toward the equator to increase the tangential speed

An astronaut hovers in space beside a rotating asteroid. Both he or she and the center of mass of the asteroid are at relative rest. If the asteroid is in earth orbit, does the astronaut also have to be in Earth's orbit? Why / Why not?Explain to me!!!!!

yes --> if they are hovering together they must be rotating together

If the earth were to rotate more slowly about its axis, what would happen to your weight? Why?

it would increase --> lower tangential speed

A possible space habitat of the future is a doughnut shaped craft rotating about its axis. What is the relative gravitational field at the axis of this habitat?

0

Mrs. Corlew loves to make vanilla frappuccinos in her new blender. If she blends an 8.00 g ice cube on high so that it spins around the blender at 23.0 m/s with a centripetal force of 11.2 N. What is the radius of the blender?

0.378 m

What tangential speed must a 65.0 kg person have in order to feel weightless in a carnival ride that has a radius of 20.00 m and spins with 3.000 rotations in one minute?

14.0 m/s

A space habitat is designed so that the variation in g between a person's head and feet is less than 2/1000 g. If the person is 5 m tall, then what is the radius of the habitat?

2,500 m

To test their stamina, astronauts are subjected to many rigorous physical tests before they fly in space. One such test involves spinning the astronauts in a device called a centrifuge that subjects them to accelerations far greater than gravity. With what linear speed would an astronaut have to spin in order to experience an acceleration of 3 g's at a radius of 10.0 m?

20 m/s

When an irregularly shaped object is thrown spinning through the air, what path does its center of gravity follow?

A straight line that is in a parabolic path

What is a straight line about which rotation takes place?

Axis

If a plumb line is dropped from a suspension point of a square piece of cardboard, what can you say about the amount of weight and mass on each side of the line? Where will the center of gravity be in relation to the line?

Half of the weight and also half of the mass will be on either side of the line and the center of gravity will be directly along the line

If an object is in neutral equilibrium, any displacement will do what to its center of gravity?

It's center of gravity will remain unchanged

What must be true of an object's center of gravity if it topples?

Its center of gravity must be outside of its area of support

Inside a futuristic rotating donut-shaped space station, the rotation creates a normal support force that feels like gravity. If you would begin to sprint in the direction that the station rotates, what happens to the magnitude of the simulated gravity that you feel?

It increases ---> higher tangential speed

Where is the center of mass of the solar system? Is it in the same location as the center of gravity? Why or Why not?

It varies as the planets move but usually slightly outside of the center of the sun. The center of gravity is usually at the sun's actually center where the most mass can be located.

Which has greater rotational speed, ladybug near the outside of a turntable or inchworm near the inside? Why?

Neither→ They both have the the same rotational speed because both have the same period.

Do passengers on a rotating platform of a carnival ride need to be strapped in to keep from falling out? Why or why not?

No --> the reaction force of the ride pushing inward against the their weight which is pushing the person outward which actually keeps the person in

Is the center of gravity of an object equivalent to the object's geometric center? Is it equivalent to its center of mass? Why or Why not?

No--.> it has more to do with weight than shape No--> usually true, but not for very large objects that may have variations in gravity

If you whirl a tennis ball on the end of a string and the string suddenly breaks, in what direction will the ball move?

The ball will fly off, tangent to its circular path

What is a Center of Gravity?

The center of Gravity is a point located at an object's average position of weight

An inchworm rests on the bottom of a cup that is being whirled horizontally on the end of a string. Since the inchworm, like the cup, moves in a circle, there must be a force on it. What exerts this force?

The cup

Which has greater linear speed, a ladybug near the outside of a turntable or an inchworm near the inside? Why?

The ladybug near the outside because it covers a larger distance during each rotation.

A period of rotational is the time it takes for what to happen?

The time it takes for one full rotation/revolution of an object

If you try to pick a small object up off the floor while standing flat against a wall, you probably will fall over. Why?

The wall doesn't allow you to change your body position in order to keep your center of gravity inside your area of support so your center of gravity goes outside your feet support and you will fall.

Luigi twirls a round piece of pizza dough overhead with a frequency of 60 revolutions per minute. a) Find the linear speed of a stray piece of pepperoni stuck on the dough 10 cm from the pizza's center. b) In what direction will the pepperoni move if it flies off while the pizza is spinning? Explain the reason for your answer.

a) 60 cm/s b) it will go tangent to the pizza because the pepperoni's inertia is tangent to the circle

A 3.20 kg hawk circles overhead in search of prey. a) If the hawk circles once every 10.0 s in a circle 12.0 m in radius, what is the linear speed of the hawk? b) What centripetal force allows him to remain in a circle? c) What is providing the centripetal force?

a) 7.54 N b) 15.2 N c) the air pushing up against his wings

When you carry a heavy load with one arm, why do you tend to hold your free arm away from your body?

in order to move the center of gravity of your body and the load back over your support base which is your feet

As the rotational speed of a space habitat increases, what happens to the weight of people inside? Why?

increases→ they are pushed down against the scale

What is the direction of the force that acts on lettuce while it's spinning in a salad spinner? What is this force called?

inward→ this is called centripetal force

Any object thrown into the air rotates about what point?

it center of gravity

If an object is in unstable equilibrium, any displacement will do what to its center of gravity?

lower it

A box resting on the floor is in what kind of equilibrium?

neutral (as long as the displacement is pushing it across the floor, not lifting it)

Will a child on a turning merry-go-round make more turns per minute if he or she walks toward the center of the merry-go-round? Why or why not?

no --> rotational speed is equal at all points along a rotating object

If an object is in stable equilibrium, any displacement will do what to its center of gravity?

raise it

You push a ping pong beneath the surface of water in a glass of water. What happens to the center of gravity of the glass of water?

the center of gravity rises

Define Rotational Speed.

the number of rotations per unit of time

If a swing on a carnival ride travels in a circle with constant speed, in what direction is the net force on the swing directed?

toward the center of the ride

Where is the center of mass of a human located?

usually 2-3 cm below the navel(belly button), but it changes based on body orientation

Based on stability concepts, you would expect a very tall building to have what?===== why?????

very deep underground supports