Physics

Which is easier to get swinging: a baseball bat held at the narrow end or a bat held closer to the massive end (choked up)?

A bat held closer to the massive end is easier to get swinging

The softball because it has the smallest rotational inertia compared with its mass

A softball and a basketball start from rest and roll down an incline. WHich ball reaches the bottoms first? Defend your answer.

Which will have the greater acceleration rolling down an incline: a hoop or a solid disk?

A solid disk has less rotational inertial and will have the greater acceleration

Yes. Interior tides are caused by unequal forces on opposite sides of Earth's interior

Do tides occur in the molten interior of Earth for the same reason that tides occur in the oceans?

Your weight would increase

If Earth shrank but there was no change in its mass, what would happen to your weight at the surface?

Angular momentum=mvr= (80 kg)(6 m/s)(2 m) =960 kg x m^2/s

If a person's speed doubles and all else remains the same, what will be the person's angular momentum?

What is rotational inertia, and how is it similar to inertia as studied in earlier chapters?

Rotational inertia is the resistance to a change in rotational motion. It is similar to plane inertia, which is a resistance to change in velocity

How can gravity be simulated in an orbiting space station?

Rotational motion results in a centrifugal force that behaves like the force of gravityHow can gravity be simulated in an orbiting space station?

In accord with the inverse-square law, four times as far from the Earth's center diminishes the value of g to g/42, or g/16, or 0.6 m/s2.

Show that the gravitational force between two planets is quadrupled if the masses of both planets are doubled but the distance between them stays the same

Fom F=G2m2MI(2d^2) = 4/4 (GmMId^2), with the same force of gravoitation.

Show that there is no change in the force of gravity between two objects when their masses are doubled and the distance between them is also doubled.

The occupants are without a support force

Why are international Space Station occupants weightless when they are firmly in the grip of Earth's gravity?

One side is closer

Why do both the Sun and the Moon exert a greater gravitational force on one side of Earth than on the other?

The speed of satellite doesn't change when there's no component of gravitational force in the direction of its motion.

Why doesn't the force of gravity change the speed of a satellite in circular orbit?

A black hole is invisible because even light cannot escape it

Why is a black hole invisible?

A satellite must remain above the atmosphere because air resistance would not only slow it down but incinerate it at its high speed. A satellite must not have to contend with either of these.

Why is it important that the projectile in the preceding question be above the Earth's atmosphere?

No. No lever arms would exist between Earth's gravitational pull and the Moon's axis

Would a torque on the Moon occur if the moon were spherical, with both its center of mass and center of gravity in the same location?

The springs would be more compressed when accelerating upward; less compressed when accelerating downward.

Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was accelerating upward? Downward?

If you hang at rest by your hands from a vertical rope, where is your center of gravity with respect to the rope?

Your CG is beneath the rope

A satellite has the greatest speed when nearest Earth, and the lowest speed when farthest away.

At what part of an elliptical orbit does an Earth satellite have the greatest speed? The lowest speed?

F= (80 kg) (3 m/s)^2 /2 m =360 N

Calculate the force of friction that keeps an 80-kg person sitting on the edge of a horizontal rotating platform when the person sits 2 m from the center of the platform and has a tangential speed of m m/s.

MV^s/R 7.2 N

Calculate the tension in a horizontal string that whirls a 2-kg toy in a circle of radius 2.5 m when it moves at 3 m/s on an icy surface.

No. By definition, a torque requires force and a lever arm

Can a force produce a torque when there is no level arm?

It is g = GM/r2 = (6.67 x 10-11) (3.0 x 1030)/(8.0 x 103)2 = 3.1 x 10^12 m/s2, 300 billion times g on Earth.

Find the change in the force of gravity between two planets when the distance between them becomes 10 times smaller.

The period for satellites at higher altitudes is longer than 90 minutes.

For orbits of greater altitude, is the period longer or shorter?

What is the relationship between the center of gravity and the support base for an object that is in stable equilibrium?

For stable equilibrium, the CG must be above the support base and not extend beyond it

A projectile can fall around the Earth if it has sufficient tangential speed so that its curve downward is no sharper than that of Earth's curvature.

How can a projectile "fall around the Earth"?

The thickness is one-fourth as much

How does the thickness of paint sprayed on a surface change when the sprayer is held twice as far away?

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

In attempting to do so, your CG extends beyond your support base, so you toppleIn terms of center of gravity, support base, and torque, why can't you stand with your heels and back to a wall and then bend over to touch your toes and return to your stand-up position?

The Moon falls away from the straight line it would follow if there were no gravitational force acting on it

In what sense does the Moon "fall"?

If you are not wearing a seatbelt in a car that rounds a curve, and you slide across your seat and slam into the car door, what kind of force is responsible for your slide: centripetal, centrifugal, or no force? Why is the correct answer "no force"?

No force is responsible; you tend to move forward in a straight line and the car curves into youIf you are not wearing a seatbelt in a car that rounds a curve, and you slide across your seat and slam into the car door, what kind of force is responsible for your slide: centripetal, centrifugal, or no force? Why is the correct answer "no force"?

As distance increases between most of the mass of an object and its center of rotation, does rotational inertia increase or decrease?

Rotational inertia increases with increasing distanceAs distance increases between most of the mass of an object and its center of rotation, does rotational inertia increase or decrease?

From F=GmMid^2, three times d squared is 9d^2, which means the force is one ninth of surface weight

Suppose you stood atop a ladder so tall that you were 3 times as far from Earth's center as you presently are, Show that your weight would be 1/9 of its present value.

What are the units of measurement for tangential speed ? For rotational speed ?

Tangential speed is measured in meters per second, rotational speed is measured in RPM

What is the law of inertia for rotating systems in terms of angular momentum?

The angular momentum of a system remains constant when no net torque actsWhat is the law of inertia for rotating systems in terms of angular momentum?

Is it an inward force or an outward force that is exerted on the clothes during the spin cycle of an automatic washing machine?

The force on the clothes is inward

What is meant by the "lever arm" of a torque?

The lever arm is the shortest distance between the applied force and rotational axis

If you toss a stick into the air, it appears to wobble all over the place. Specifically, about what place does it wobble?

The stick wobbles, spins really, about its CM or CG

A tapered cup rolled on a flat surface makes a circular path. What does this tell you about the tangential speed of the rim of the wide end of the cup compared with that of the rim of the narrow end?

The wide end has a greater tangential speed than the narrow end

Calculate the torque produced by the same 50-N force when a pipe extends the length of the wrench to .5 m.

Torque= .5m X 50 N = 25 m x NCalculate the torque produced by the same 50-N force when a pipe extends the length of the wrench to .5 m.

Calculate the torque produced by a 50-N perpendicular force at the end of a .2-m-long wrench.

Torque= lever arm X force Torque= .2 X 50 Torque=10 m x NCalculate the torque produced by a 50-N perpendicular force at the end of a .2-m-long wrench.

Kepler discovered that the period squared was proportional to the radial distance cubed.

What did Kepler discover about the periods of planets and their distances from the Sun?

Newton discovered that gravity is universal

What did Newton discover about gravity?

At Earth's center, its gravitational field is zero

What is the magnitude of the gravitational field at Earth's center?

The gravitational force is 6x10^-11 N

What is the magnitude of the gravitational force between two 1-kg bodies that are 1 m apart?

Anywhere inside a hollow planet the gravitational field of the planet would be zero

What would be the magnitude of the gravitational field anywhere inside a hollow, spherical planet?

Actually the mass of Earth could then be calculated, but weighing of Earth hit a more popular tone

When G was first measured by Henry Cavendish, newspapers of the time hailed his experiments as the "weighing Earth experiment," Why?

Your weight is measured as mg when you are firmly supported and in equilibrium

When is your weight measured as mg?

No, because there is zero lever arm about the CM. Zero lever arm means zero torque

When the line of action of a force intersects the center of mass of an object, can that force produce a torque about the object's center of mass?