What class of motion did Aristotle attribute to the Moon?
answer
The Moon has a Natural class of motion
question
What state of motion did Aristotle attribute to Earth?
answer
The Earth has a Natural class of motion
question
What relationship between the Sun and Earth did Copernicus formulate?
answer
The Earth revolved in a circle about the Sun.
question
What did Galileo discover in his legendary experiment on the Leaning Tower of Pisa?
answer
Galileo found that a heavier stone does not fall significantly faster than a lighter one.
question
What did Galileo discover about moving bodies and force in his experiments with inclined planes?
answer
In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.
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What is inertia?
answer
Inertia is the tendency of a body to maintain its state of motion in the absence of applied forces.
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How does Newton's first law of motion relate to Galileo's concept of inertia?
answer
Newton refined Galileo's concept of inertia and made it his first law of motion.
question
What type of path does a moving object follow in the absence of a force?
answer
It continues to move in a straight line at a constant speed.
question
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?
answer
The net force is 70 pounds to the right
question
Why do we say that force is a vector quantity?
answer
A force has a magnitude and a direction.
question
According to the parallelogram rule, what quantity is represented by the diagonal of a constructed parallelogram?
answer
The diagonal is the resultant, or sum, of two vectors.
question
What is the resultant of a pair of one pound forces at right angles to each other?
answer
The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors.
question
Consider Nellie hanging at rest in Figure 2.11. If the ropes were vertical, with no angle involved, what would be the tension in each rope?
answer
The tension in each rope would be half of the gravity force.
question
What are the units for force?
answer
Force can be expressed in newtons or pounds.
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What is the net force on an object that is pulled with forces of 80 newtons to the right and 80 newtons to the left?
answer
The net force is zero newtons.
question
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?
answer
The net force is zero newtons.
question
What does it mean to say something is in mechanical equilibrium?
answer
An object in mechanical equilibrium experiences a zero net force.
question
State the equilibrium rule for forces in symbolic notation
answer
ΣF = 0
question
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?
answer
15 newtons up
question
When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale?
answer
Your weight is equal in magnitude and opposite in direction to the support force from the scale.
question
A bowling ball at rest is in equilibrium. Is the ball in equilibrium when it moves at constant speed in a straight-line path?
answer
Yes, the bowling ball is in equilibrium because ΣF = 0.
question
What is the net force on an object in either static or dynamic equilibrium?
answer
The net force is zero.
question
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?
answer
The frictional force on the crate is 100 N opposite the direction of motion.
question
What concept was not understood in the 16th century when people couldn't conceive of a moving Earth?
answer
They did not understand inertia.
question
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?
answer
It continues to move at 30km/s relative to the Sun, but it has a speed of 0 km/s relative to the ground.
question
Stand next to a wall that travels at 30 km/s relative to the Sun. With your feet on the ground, you also travel at the same 30 km/s. Do you maintain this speed when your feet leave the ground? What concept supports your answer?
answer
When you jump, you continue to move at 30 km/s due to your inertia.
question
Your friend says that inertia is a force that keeps things in their place, either at rest or in motion. Do you agree? Why or why not?
answer
No, I dont agree because Inertia is a PROPERTY of objects. Inertia is property that makes objects want to keep doing what theyre doing.
question
Consider the normal force on a book at rest on a tabletop. If the table is tilted so that the surface forms an inclined plane, will the magnitude of the normal force change? If so, how?
answer
The normal force is always perpendicular to the object. So if the table is tilted the Normal Force will also tilt with the book so it is pointed at an angle relative to the horizontal.
question
A ball rolling along a floor doesn't continue rolling indefinitely. Is it because it is seeking a place of rest or because some force is acting upon it?
If the latter, identify the force.
answer
It is because some force is acting upon it.
The force is friction
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