Chapter 3

Does a force always produce motion? Explain.

An old party trick is to pull a tablecloth out from under dishes and glasses on a table. Explain how this is done without pulling the dishes and glasses with the cloth.

To tighten the loose head of a hammer, the base of the handle is sometimes struck on a hard surface (O Fig. 3.24). Explain the physics behind this maneuver.

Explain the principle of automobile seat belts in terms of Newton's first law.

Describe the relationship between (a) force and acceleration, and (b) mass and acceleration.

Can an object be at rest if forces are being applied to it? Explain.

If no forces are acting on an object, can the object be in motion? Explain.

The coefficient of kinetic friction is generally lower than the coefficient of static friction, Why is this?

A \(10 \mathrm{lb}\) rock and a \(1 \mathrm{lb}\) rock are dropped simultaneously from the same height. (a) Some say that because the \(10 \mathrm{lb}\) rock has ten times as much force acting on it, it should reach the ground first. Do you agree? (b) Describe the situation if the rocks were dropped by an astronaut on the Moon.

When a rocket blasts off, is it the fiery exhaust gases "pushing against" the launch pad that causes the rocket to lift off? Explain.

If an object is accelerating, does Newton's third law apply? Explain.

Explain the kick of a rifle in terms of Newton's third law. Do the masses of the gun and the bullet make a difference?

Show that the universal gravitational constant \(G\) has units of \(\mathrm{N} \cdot \mathrm{m}^{2} / \mathrm{kg}^{2}\)

The gravitational force is said to have an infinite range. What does this mean?

Are astronauts "weightless" in a spacecraft orbiting the Earth? Explain.

Is “zero g” possible? Explain.

As learned in Chapter \(1.5\), a liter of water has a mass of one kilogram. A thin, closed plastic bag (negligible weight) with a liter of water in it is lowered into a lake by means of a string. When fully submerged, how much force would you have to exert on the string to prevent the bag from sinking further?

Is it easier for a large person to float in a lake than a small person? Explain.

Why must a helium balloon be held with a string?

What are the units of linear momentum?

Explain how the conservation of linear momentum follows directly from Newton's first law of motion.

When a high diver in a swimming event springs from the board and "tucks in," a rapid spin results. Why is this?