Physics Ch.2

What is the net force when a pair of 5-N forces simultaneously act in the same direction on an object?

10 N

Consider a book that weighs 15 N at rest on a flat table. How many newtons of support force does the table exert on the book?

15 newtons up

Why do we say that force is a vector quantity?

A force has a magnitude and a direction.

What does it mean to say something is in mechanical equilibrium?

An object in mechanical equilibrium experiences a zero net force.

What are the units for force?

Force can be expressed in newtons or pounds

What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa?

Galileo found that a heavier stone does not fall significantly faster than a lighter one.

What did Galileo discover about moving bodies and force in his experiments with inclined planes?

In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.

A bird sitting in a tree is traveling at 30 km/s relative to the faraway Sun. When the bird drops to the ground below, does it still move at 30 km/s, or does this speed become zero?

It continues to move at 30km/s relative to the Sun, but it has a speed of 0 km/s relative to the ground.

What type of path does a moving object follow in the absence of a force?

It continues to move in a straight line at a constant speed.

What two classes of motion did Aristotle advocate?

Natural motion and violent motion

How does Newton's first law of motion relate to Galileo's concept of inertia?

Newton refined Galileo's concept of inertia and made it his first law of motion.

Which of Newton's laws does the equilibrium rule illustrate?

Newton's first law

What relationship between the Sun and Earth did Copernicus formulate?

The Earth revolved in a circle about the Sun.

What did Copernicus say about the motion of the Sun?

The Sun is stationary and Earth circles it.

According to the parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram?

The diagonal is the resultant, or sum, of two vectors.

If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate?

The frictional force on the crate is 100 N opposite the direction of motion.

What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force?

The net force is 70 pounds to the right.

What is the net force on an object in either static or dynamic equilibrium?

The net force is zero

What is the resultant of a pair of one pound forces at right angles to each other?

The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors.

What concept was not understood in the 16th century when people couldn't conceive of a moving Earth?

They did not understand inertia.

A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight-line path?

Yes, the bowling ball is in equilibrium because ΣF = 0.

When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale?

Your weight is equal in magnitude and opposite in direction to the support force from the scale.

Newton said that something was needed to change the motion of an object. A clear reading of his first law tells us that what is needed is ______.

a non-zero net force

What is the net force on a bag pulled down by gravity with a force of 18 newtons and pulled upward by a rope with a force of 18 newtons?

zero

State the equilibrium rule for forces in symbolic notation

ΣF = 0