PY 131 Chapter 8 Conceptual Academy

**A child that sits on a horse near the outer edge of a merry-go-round has a greater**

A child that sits on a horse near the outer edge of a merry-go-round has a greater

A child that sits on a horse near the outer edge of a merry-go-round has a greater

linear speed.

To determine the direction of travel for a coin sliding off the edge of a rotating record, Paul thought it a good idea to use

talcum powder.

Rotational inertia depends upon

mass and distance.

Center of gravity and center of mass are

most often in the same location.

Which example in this lesson showed where the CG of an object lies outside the matter making up the object?

L-shaped piece of wood

Torque tends to produce a change in

rotation.

**How does the Moon's center of gravity compare to its center of mass? Its center of gravity is**

closer to Earth.

When Nellie swings a can at constant speed in an overhead circle, the can

is undergoing acceleration.

The direction of force that keeps the can circling is toward the

inside of the circular path.

When a car drives along a properly-banked road, the force holding the car in a circular path is

the radial component of the normal force.

The direction of centrifugal force acting on a bug in a circularly-moving tin can is toward the

outside of the circular path.

The equations for centripetal and centrifugal force are

the same

Physicists call centrifugal force ficticious because

there is no action-reaction counterpart.

In this lesson we see that the formula for angular momentum is the equation for linear momentum

multiplied by radial distance r.

A change in angular momentum requires a

torque.

Angular momentum is nicely illustrated by

figure skaters.

Angular momentum is rotational inertia multiplied by rotational

velocity.

Angular momentum is always

conserved

The tangential speed on the outer edge of a rotating carousel is

greater than toward the center.

Rotational inertia about the midpoint of an object becomes greater with

increased mass and increased distance to mass concentration.

The torque exerted by a crowbar on an object increases with increased

force and leverage distance.

The center of gravity of a basketball is located

at its geometrical center.

When a rock tied to a string is whirled in a horizontal circle, doubling the speed

quadruples the tension in the string.

When a rock tied to a string whirled in a horizontal circle somehow doubles in mass but keeps the same speed, the string tension

doubles

Consider someone in a rotating space habitat. The outward force felt by the person

has no reaction counterpart.

Consider someone in a rotating space habitat. Rotational motion provides

a support force

What is required to change the angular momentum of a system?

external torque.

When the rotational speed of a rotating system doubles, it angular momentum

doubles.

A can filled with water and an identical can filled with solid ice roll down an incline. The one to travel quickest to the bottom is the can filled with

water

It is easiest to rotate in a somersault when your body is

balled up

A donut shaped space station spins so that within the outer rim, astronauts experience a gravity of one "g". At a higher level of 1/4 "g", there is a swimming pool. At this level, a diver who can jump 1 meter high in the outer rim, should be able to jump

4 m

What do you know about the center of gravity of a baseball bat balanced on a fulcrum?

\n **It's above the fulcrum.**

The reason balls roll downhill is primarily because of

\n **an unbalanced torque.**

Balancing a broom on its end is easier when the heavier brush side of the broom is

\n **highest, farthest from your hand.**

Placing super tall tires on your car will make your speedometer show a speed that is

\n **lower than it is actually.**

In balancing a horizontal broom, your finger supports the broom closer to the bristles. Saw the broom at that point to make two pieces. Which piece is heavier?

the bristles part

The wheels of a bicycle have a circumference of 2 meters. Upon riding the bicycle so that the wheels revolve once a second, your speed is

2 m/s

A baseball bat tossed into the air wobbles around its

center of mass

When a torque acts upon an object, it tends to produce

rotation

To help a train travel along a curved track, the rim edge of all railroad train wheels are tapered with the outer edge being a bit narrower than the inner edge. Two wheels opposite each other and connected by the same axel can

**in effect, vary their diameters. AND travel at different linear speeds for the same rotational speed.**

**Both of these are correct.**

An 8 meter heavy wooden plank laying flat extends 2 meters over a cliff. You find that you can stand on the overhang 1 meter from the cliff's edge, just barely. Any farther out, you would fall. This tells you that the mass of the plank is

**half your mass.**

(you are standing on 1/2 of the plank that is out)

A truck driving at constant speed in a circle has a net force

**directed toward the center of the curve.**

To help a train travel along a curved track, the rim edge of all railroad train wheels are tapered with the outer edge being a bit narrower than the inner edge. Thus, when making a curve, different parts of the rim edge

\n **cover a different distance in the same time.**

To play solitary seesaw, a girl places a 4 meter wooden plank over a rock. Sitting on one end, she is balanced by the weight of 3.5 meters of the plank on the opposite side. How does her mass compare to the mass of the plank?

\n **Her mass is greater than the mass of the seesaw.**

A string of lights is whirled overhead in a circular path. The bulb at the end of the string moves how much faster than the bulb in the string's middle?

**Twice as fast.**

The Leaning Tower of Pisa has not fallen over. From this we can conclude that its center of gravity is

\n **above a place of support.**

A blank music compact disc (CD) has a center of gravity that is

**at the center hole of the disk.**

A ring and a coin of the same mass and diameter roll down an incline. If released at the same time, the first one to get to the bottom will be the

coin

A meter stick standing freely on its end will fall over. Attach a heavy lump of clay to the top end, however, and the falling time will be

**more.**

What kind of screwdriver is best for removing a screw that is held tight?

\n **One with a wide handle.**

A donut shaped space habitat rotates to provide a sense of gravity to astronauts living inside. As the rotational speed increases, the astronauts apparent weight

\n **also increases.**

A mass of 1 kilogram is suspended from the end of a meter stick at the 100 cm mark. Placed on a fulcrum at the 75 cm mark, the meter stick is balanced. The mass of the meter stick must be

1 kg

Two flywheels are of the same size and shape. One, however, is twice as massive, which means its rotational inertia is

\n **two times the other's.**

A mouse sits 1 inch from the center of a record player moving at 33 rpm. If she instead sat 2 inches from the center, her linear speed would

double

The rotational speed of a record player is doubled. A mouse sitting on the outer edge will have a linear speed that

\n **is also doubled.**

To make balancing easier, a tightrope walker will want the pole he carries to be

**drooping.**

In a space colony spacecraft, humans will survive best with a gravitational field of

g

A rocket ship weighs less at the equator compared to its weight at the north or south pole. Why?

\n **The spin of the Earth.**

A donut shaped space station spins so that within the outer rim, astronauts experience a gravity of one "g". For recreation, the astronauts have asked for a bowling alley. To best mimick a bowling experience on Earth, how should the alley be oriented?

\n **Parallel to the rim facing in the direction of rotation so the ball feels heavier upon throwing.**

A disk, a ring, and a ball all of the same diameter and are released at the same time to roll down an incline. The first to reach the bottom is the

sphere

What would happen to the apparent weight of the average Californian if Earth slowed its rate of rotation?

**It would increase.**

A spider monkey has a long and heavy tail, which helps it to change its

\n **center of gravity.**

A donut shaped space station spins so that within the outer rim, astronauts experience a gravity of one "g". An astronaut who climbs halfway to the axis of spin will experience

\n **one-half "g".**

To help a train travel along a curved track, the rim edge of all railroad train wheels are tapered with the outer edge being a bit narrower than the inner edge Because of this, the tangential speed of the narrower outer edge of a rolling wheel is

\n **smaller than that of the wide part.**

Jack and Jill sit perfectly balanced on a frictionless seesaw. Jack leans forward, which causes him to

rise

Two boys are balanced on a see saw. One boy, who is three times as heavy, sits

\n **1/3 the distance from the fulcrum.**

The human body has a center of mass located at a point

\n **that changes as a person bends over.**

Two peanut butter jars, one empty and one full, roll down a ramp. The one to reach the bottom quickest is the

\n **the filled jar**

If you double the length of a wrench handle, you effectively multiply the torque by

two

The reality of centrifugal force becomes apparent to some one in a frame of reference that is

rotating

What if Earth had two identical moons in the same circular orbit, each always on opposite sides as far apart from each other as possible. For this Earth-Double Moon system, the center of gravity would be located where?

\n **At the center of the Earth.**

Two flywheels are of the same mass and shape. One, however, has a diameter twice the size, which means its rotational inertia is

\n **four times the other's.**

While running, your leg has greater rotational inertia when it is

straight

A disk and a ring of the same diameter and width are released at the same time to roll down an incline. The first to reach the bottom

\n **is the disk.**

In a carnival Ferris wheel you are sitting 10 meters from the axis. If it takes 60 seconds to complete a rotation, then your linear speed is

\n **62.8 m/min.**

With a merry-go-round, you'll find the greatest linear speed with a horse located

\n **near the outside.**

In meters per second, the faster horse of a merry-go-round is the

\n **outside horse**

A football of the American type will not topple end over end when kicked

\n **through its center of gravity.**

A small boy places a rock under the middle of a long wood plank, sits near one end and his mother sits near the opposite end. To balance each other. A mother and her small boy want to balance perfectly on a seesaw. They start by sitting on the middle of each side, which doesn't work. What should they do?

**None of these choices would work.**

What must be true of the resultant force and/or torques for a system in mechanical equilibrium?

\n **The resultant forces and torques must both be zero.**

A massive flywheel of industrial quality has more rotational inertia when the bulk of its mass is

\n **nearest the rim.**