Week 1

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? Identify that force.

-It is because some force is acting upon it -Friction force

Which of the following is a vector quantity?

-acceleration -force -momentum -displacement -velocity

Two people each pull with 300 N on a rope in a tug of war. What is the net force on the rope?

0 N

How much force is exerted on each person by the rope?

300 N

The sum of the x components of vectors A and B in Figure 1 is _________.

4

If the strong man exerts a downward force of 800 N on the rope, how much upward force is exerted on the block?

800 N

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

A stubborn stump is pulled by a pair of ropes, each with a force of 200 N, but at different angles as shown. From greatest to least, rank the total force from the ropes on the stump.

B, A, C

The weights of Burl, Paul, and the scaffold produce tensions in the supporting ropes. Rank the tension in the left rope, from most to least, in the three situations. A,B, and C.

C, B, A

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 demonstrate in his Leaning Tower of Pisa experiment?

He demonstrated that light and heavy objects gain the same amount of speed when falling

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

What is inertia?

Inertia is the tendency of a body to maintain its state of motion in the absence of applied forces

Is the tension in the rope less than, equal to, or greater than 50 N?

Less

Which of the choices shows the correct resultant of adding the two vectors A and B shown in Figure 2?

Long arrow pointing upward left

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

Are there any quantities of the following, which are neither vector quantities nor scalar quantities: force, age, acceleration, temperature?

No

If you toss a coin straight upward while riding in a train, where does the coin land when the train is rounding a corner?

The coin lands off to the side of you

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 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?

The net force is zero newtons

Some alphabet letter are floating in a bowl of soup. You want to move a letter that is far away from you closer to you. How could you rotate the bowl to do that?

Unfortunately, neither rotating the bowl clockwise nor rotating it counterclockwise will work

The sketch shows a painter's scaffold in mechanical equilibrium. The person in the middle weighs 500N, and the tensions in each rope are 400N. What is the weight of the scaffold?

W=300N

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?

When you jump, you continue to move at 30 km/s due to your inertia

According to Newton's first law, when the net force acting on an object is zero, the object must ________.

have constant velocity

The sum of two vectors is the largest when the two vectors are _________.

pointing in the same direction

Scalar quantities:

temperature & age

State the equilibrium rule for forces in symbolic notation.

ΣF = 0

Imagine holding a basketball in both hands, throwing it straight up as high as you can, and then catching it when it falls. At which points in time does a zero net force act on the ball? Ignore air resistance. Check all that apply.

-When you hold the ball still in your hands before it is thrown -When you hold the ball still in your hands after catching it

Three pucks, A, B, and C, are shown sliding across ice at the noted speeds. Air and friction forces are negligible. 1) Rank them, from greatest to least, by the force needed to keep them moving. 2) Rank them, from greatest to least, by the force needed to stop them in the same time interval.

1) All aligned 2) C (6 m/s), B (4m/s), A (2 m/s)

Different materials, A, B, C, and D, rest on a table: 12 kg sand, 15 kg iron, 10 kg water, 2 kg pillow. 1) From greatest to least, rank them by how much they resist being set into motion. 2) From greatest to least, rank them by the support (normal) force the table exerts on them.

1) B(iron), A (sand), C (water), D (pillow) 2) NB, NA, NC, ND

Nellie Newton hangs motionless by one hand from a clothesline. 1) Which side of the line, a or b, has the greater horizontal component of tension? A or B 2) Which side of the line, A or B, has the greater vertical component of tension? 3) Which side of the line, A or B, has the greater tension?

1) Both aligned 2) A, B 3) A, B

Suppose that you jounce (bounce in a jolting fashion) up and down while weighing yourself on a bathroom scale. 1) Which varies: the upward support force or the force of gravity on you? 2) Why is your weight reading best shown when you stand at rest on the scale?

1) The upward support force 2) Only when you are in equilibrium, the support force exerted on you by the bathroom scale will correctly show your weight

Rank the magnitudes of the net force on the block from most to least in the four situations A, B, C, and D,

12N C 4N, 10N A 5N, 7N B 3N, 3N D 3N

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

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

It continues to move at 30 km/s relative to the Sun, but it has a speed of 0km/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 class of motion did Aristotle attribute to the Moon?

Natural

What state of motion did Aristotle attribute to Earth?

Natural

Consider the video demonstration that you just watched. Which of the following changes would make it more likely for the ball to hit both the white can and the green can?

None of the above

A force of gravity pulls downward on a book on a table. What force prevents the book from accelerating downward?

Normal

A different scaffold that weighs 400N supports two painters, one 500N and the other 400N. The reading in the left scale is 800N. What is the reading in the right hand scale?

T=500N

What relationship between the Sun and the 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

Dr. Hewitt has clay "blobs" hanging on either side of his head in this video. When he turns around, what happens to the blobs?

The blobs tend to stay where they were

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

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

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?

The net force is zero newtons

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

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?

The tension in each rope would be half of the gravity force

Will the tension in the clothesline be greater if the line sags a lot or if it sags a little?

The tension will be greater for a small sag

What can you correctly say about a pair of vectors that add together to equal zero?

The vectors are equal in magnitude, and are opposite in direction

When Dr. Hewitt pulls the tablecloth, why do the items on the tablecloth do what they do?

Their inertia is sufficient to keep them there

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

They did not understand inertia

Why do the alphabet letters tend to do what they do when you rotate the bowl?

They have inertia - the tendency of an object at rest to stay at rest

Why do the clay blobs do what they do when Dr. Hewitt turns around?

They have inertia - the tendency of an object at rest to stay at rest

When Dr. Hewitt pulls the tablecloth, what happens to the items on the tablecloth?

They tend to stay where they were

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

You tell your friend about the neat tablecloth trick that Dr. Hewitt demonstrated. Your friend tries to repeat this trick at home and later complains to you that it failed. Which of the following is most likely the reason that it failed?

Your friend pulled the tablecloth too slowly

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

Vector quantities:

acceleration & force

An elevator moves straight upward at a constant speed. Newton's first law predicts that the net force acting on the elevator will ________.

be zero

Recall the portion of the video in which the girl pushes her brother on the sled at constant velocity. The pushing force she exerts on the sled is ________ the frictional force the ground exerts on the sled.

equal to