physcis

Perky (left) and Sneezlee (right) have the same mass and nicely balance at opposite ends of a seesaw. For the three positions, rank the length of the lever arm between Perky and the center of the seesaw from longest to shortest.

A=B=C

In what direction should a force be applied to produce maximum torque?

At a right angle to the lever arm

When Suzie gradually increases the angle of the incline, the uniform blocks of wood begin to topple (there is enough friction to keep them from sliding). Rank the order in which the blocks tip from first to last

B,A,C

Why does the Leaning Tower of Pisa not topple?

Because its CG is above a support base

Three people stand with their backs against a wall. They are all agile and in good physical condition. Their task is to lean over and touch their toes without toppling over. Rank their chances for success from highest to lowest

C,A,B

In a physics lab you find four different vertically mounted cart wheels that are not free to rotate. Each has a block that hangs from a string wrapped around the wheel. Rank the torques these blocks produce about the wheel axes from greatest to least.

C,D,A,B

You hold a meterstick with the same suspended masses at the angles shown. Rank the torque needed to keep the stick steady from largest to smallest.

D,A,C,B

where is the center of gravity of an object that hangs in equilibrium? for an object that stands in equilibrium?

For a suspended object, the CG is below the point of suspension. For a standing object, the CG is above the support base.

How does torque differ from force?

Force is a push that can accelerate objects; torque is force x lever arm that can rotate objects.

To kick a football so that it doesn't rotate through the air, where should it be kicked relative to its center of mass?

It should be kicked in line with its center of mass, not above or below it.

What accounts for the stability of the Space Needle in Seattle?

Its CG is below ground level so in order for it to topple its CG would have to be raised

Is the gravitational potential energy more, less, or unchanged when the CG of an object is raised?

Potential energy is more when the CG is raised

Why do some high jumpers arch their bodies into a U shape when passing over the high bar?

So that their CG can pass beneath the bar; then the bar is higher than the actual jumping height!

You cannot stand with your heels and back to the wall and then lean over and touch your toes without toppling. Would either stronger legs or longer feet help you to do this? Defend your answer.

Stronger legs, no; longer feet lengthen the support base, so yes

A bottle rack that seems to defy common sense is shown in the figure. Where is the CG of the rack and bottle

The CG lies directly above the support base.

Explain why a long pole is more beneficial to a tightrope walker if the pole droops.

The CG of the pole is lowered when the pole droops. If the CG is below the rope, then there is more stability

If a container of dried beans with a table tennis ball at the bottom is shaken, what happens to the CG of the container?

The CG would lower (and the container would become more stable).

What part of an object follows a smooth path when the object is made to spin through the air or across a flat smooth surface?

The center of gravity follows the smooth path

Why is the center of mass of a baseball bat not at its midpoint?

The center of mass is not at the midpoint because one end of the bat is more massive than the other end

Which glass in the figure is unstable and will topple?

The glass on the right is unstable and will tip because its CG lies beyond the base of support.

Is the net torque changed when a partner on a seesaw stands or hangs from her end instead of sitting? (Does the lever arm change?)

The lever arm is not changed so there is no change in torque

A long track balanced like a seesaw supports a golf ball and a more massive billiard ball with a compressed spring between the two as shown in the figure. The CG of the two-ball system is therefore directly above the point of support (the triangular fulcrum). When the spring is released, the balls move away from each other. As the balls roll outward, will the track remain in balance, or will it tip? What principles do you use for your explanation?

There will be no tipping allowed because it is inversaley proportional to the masses

When are the center of gravity and center of mass of an object the same? Give an example of when they can be different.

They are the same for ordinary-sized objects and different for large objects where gravity can vary. The moon's CG is slightly closer to Earth than its center of mass.

Why does a hiker carrying a heavy backpack lean forward?

To put the CG above the feet

True or False The center of mass of an object is the point located at the object's average position of the mass.

True

True or False When balanced torques act on an object, there is no change in rotation.

True

Distinguish between unstable, stable, and neutral equilibrium.

Unstable: the CG is lowered with displacement; stable: the CG rises with displacement; neutral: the CG neither rises nor falls with displacement.

How far can an object be tipped before it topples over?

Until its CG extends beyond its support base

In terms of center of gravity, support base, and torque, why can you not stand with your heels and back to a wall and then bend over to touch your toes and return to your stand-up position?

Your CG extends beyond your support base and a torque produces rotation.

The center of gravity of your best friend is located

at different places depending on body orientation

what are the two torques

counterclockwise clockwise

lever arm

distance from the turning axis to the point of contact

When two children of different weights balance on a seesaw, they each produce

equal torques in opposite directions.

An unsupported object will topple over when its center of gravity

extends beyond the support base.

The center of mass of a donut is located

in the hole

Suppose the torque producrd by a wrench on a stubborn nut is 60 Nm If the lever arm is doubled with no change in force what is the resulting torque

it also doubles

When a stable object is made to topple over, its center of gravity

it is raised

The center of gravity of an object

may or may not lie inside the object.

Applying a longer lever arm to an object so it will rotate produces

more torque

what is torque

produces rotatioal acceleration

in term of center of gravity discuss what determines whether or not an object will fall over when tilted give examples

the center of gravity extends outside of the area of support an unbalanced torque exists and the object will topple

What part of an object follows a smooth path when the object is made to spin through the air or across a flat smooth surface?

the center of the mass

when will an object remain in rotational equilbrium

when its center of the mass is above its support

when is a torque produced

when their is leverage