PHYSICS
The large positive charge inside the shell causes equal in magnitude charges distributed on the inner and outer surfaces of the spherical shell. Which of the following figures best represents the charge distribution on the inner and outer walls of the shell? (Figure 1)
1
If an object suspended by a scale shows a weight of 3 N in air, and 2 N when submerged in water, the buoyant force on the submerged object is __________.
1 N
Three pucks, A, B, and C, are shown sliding across ice at the noted speeds. Air and ice friction forces are negligible.Part complete Rank them, from greatest to least, by the force needed to keep them moving.
1- Stacked
How much energy is given to each coulomb of charge that flows through a 1.5-V battery?
1.5 joules
Suppose that we repeat the experiment shown in the video, but we replace one of the cylinders with a cylinder that has twice the radius (and use larger containers of water). If the height of the original cylinder is hh, how deeply must we submerge the new cylinder to get the same weight reduction as in the video?
1/4 h To get the same reduction in weight, the same volume of cylinder must be submerged. The volume of a cylinder is VV= πr2hπpir2h, so if we double the radius, we must reduce the depth of immersion by a factor of four.
Part complete How much air must a 100-ton blimp displace to float and neither rise nor sink?
100 tons
Consider a point 0.5 m above the midpoint of the two charges. As you can verify by removing one of the positive charges, the electric field due to only one of the positive charges is about 18 V/m. What is the magnitude of the total electric field due to both charges at this location?
25 V/m - Notice that this number is less than twice the magnitude of the field due to each charge. This occurs because the horizontal components of the electric field due to each charge exactly cancel out (add to zero). Only the vertical components of the fields add together.
The large positive charge inside the shell causes equal in magnitude charges distributed on the inner and outer surfaces of the spherical shell. Which of the pictures best represents the charge distribution on the inner and outer walls of the shell? (Figure 1)
4
Rank, from smallest to largest, the pressures in the tank of motionless fluid shown in the figure.
A (CBD) E F
Why do we say that force is a vector quantity?
A force has a magnitude and a direction.
Distinguish between a hypothesis and a theory.
A hypothesis is an educated guess, whereas a theory encompasses well tested and verified hypotheses.
What is the test for whether a hypothesis is scientific or not?
A hypothesis is scientific if it is possible to prove it wrong.
What is a positive ion? What is a negative ion?
A positive ion is a neutral atom that has lost one or more electrons. A negative ion is a neutral atom that has gained one or more electrons.
In daily life, we see many cases of people who are caught misrepresenting things and who soon thereafter are excused and accepted by their contemporaries. How is this different in science?
A scientist who lies in a scientific publication will suffer professional excommunication.
Consider a ball at rest in the middle of a toy wagon. When the wagon is pulled forward, the ball rolls against the back of the wagon. Interpret this observation in terms of Newton's first law.
According to Newton's first law, "Every object continues in a state of rest or of uniform speed in a straight line unless acted upon by a nonzero net force." In this situation, the force is being exerted upon the wagon, pulling the wagon forward. Since the force is not exerted on the ball itself, and because of property of inertia, or resistance to change, the ball moves backward instead of forward with the wagon.
What is meant by saying that charge is quantized?
All charged objects have a charge that is an integer multiple of the charge of an electron.
How does the charge of one electron compare to that of another electron? How does it compare with the charge of a proton? How do the masses of protons and electrons compare?
All electrons have the same charge. Electron charge is equal and opposite to the proton charge. A proton has 1800 times the mass of an electron.
What does it mean to say something is in mechanical equilibrium?
An object in mechanical equilibrium experiences a zero net force.
Which of the following are scientific hypotheses?
Chlorophyll makes grass green. Tides are caused by the Moon.
A stubborn stump is pulled by a pair of ropes, each with a force of 200 N, but at different angles as shown.
Closest to 90 degrees to farthest
If the field strength is E = 9 V/m a distance of 1 mm from the charge, what is the field strength E a distance of 3 mm from the charge?
E = 1 V/m Correct. Since E∝1/r2E∝1/r2, if the distance is increased by a factor of three, the electric field is decreased by a factor of nine
A droplet of ink in an industrial ink-jet printer carries a charge of 1.9×10−10C1.9×10−10C and is deflected onto paper by a force of 2.8×10−4N2.8×10−4N. Find the strength of the electric field to produce this force.
E = 1.5×106 N/C
Testable by science:
Earth orbits the sun every 365.25 days Mars once had liquid water on its surface Bacteria acquire resistance to antibiotics through changes in their DNA. There will be a solar eclipse next Tuesday 11 a.m. People born under the sign of Sagittarius are twice as likely to be teachers as anyone else.
What happens to electrons in any charging process?
Electrons transfer from one place to another.
In lab you find that a 1-kg rock suspended above water weighs 10 N . When the rock is suspended beneath the surface of the water, the scale reads 8.0 N . What is the buoyant force on the rock?
F = 2.0 N
What are the units for force?
Force can be expressed in newtons or pounds.
Why isn't there a horizontal buoyant force on a submerged object?
Force vectors on the sides cancel one another.
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.
Not testable by science:
Hurricane Trina was an Act of God, Vince Young is the greatest quarterback of all time.
What are steps of the scientific method.
Hypothesis, predictions, and experimental findings.
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.
Why are students of the arts encouraged to learn about science and science students encouraged to learn about the arts?
Knowing both the arts and sciences makes for a wholeness in the way we view the world.
Rank them, from greatest to least, by the force needed to stop them in the same time interval.
Largest to smallest velocity
When Dr. Hewitt immerses the object in water, how does the loss of weight of the object compare with the buoyant force of the water?
Loss of weight is equal to the buoyant force.
Measurements show that there is an electric field surrounding Earth. Its magnitude is about 100 N/C at Earth's surface, and it points inward toward Earth's center. From this information, can you state whether Earth is negatively or positively charged?
Negatively charged since the magnitude of the charge points inward toward the center.
Throughout the ages, what has been the general reaction to new ideas about established "truths"?
New ideas are opposed.
How is Coulomb's law similar to Newton's law of gravitation? How is it different?
Newton's law of gravitation is attractive, whereas Coulomb's law is attractive or repulsive. Both are proportional to the inverse square of distance.
Make a small dipole by bringing the two charges very close to each other, where they are barely touching. The midpoint of the two charges should still be on one of the grid point intersections (see figure below). Measure the strength of the electric field 0.5 mm directly above the midpoint as well as 1 mm directly above. Does the strength of the electric field decrease as 1 over distance squared (1/r21/r2)?
No, it decreases more quickly with distance. - In fact, it turns out that the strength of the electric field decreases roughly as 1/r31/r3! So the field 1 mm above the midpoint is roughly eight times weaker than at 0.5 mm above the midpoint. The important lesson here is that, in general, a distribution of charges produces an electric field that is very different from that of a single charge.
Calculate the pressure a 20-N block exerts on the table it rests on if its area of contact is 50 cm2
P = 0.4 N/cm2
How does pressure relate to force?
Pressure is force per unit area.
Two point charges are separated by 5.0 cmcm . The attractive force between them is 22 NN . Suppose that the charges attracting each other have equal magnitude. Rearrange Coulomb's law and find the magnitude of each charge.
Q = 2.5×10−6 C
Using the setup from the first question, imagine that you briefly touch the negatively charged rod to the can (assume that this rod is conducting for the sake of effect). You then hold the two rods at equal distances on either side of the can. What does the can do?
Rolls toward the positively charged rod - The can acquires a net negative charge after being touched, so it is then attracted to the positively charged rod.
Now, consider the situation shown in the figure below. What does the can do?
Stays still - The polarization force is always attractive, so the can does not move.
Consider the situation in the figure below, where two charged rods are placed a distance dd on either side of an aluminum can. What does the can do?
Stays still - The positively charged rod induces a negative charge on the left side of the can, creating an attractive force between the rod and the can. However, the negatively charged rod induces an equal positive charge on the right side of the can, which creates an attractive force between the can and that rod. The net force acting on the can is zero.
A different scaffold that weighs 400 NN supports two painters, one 500 NN and the other 400 NN. The reading in the left scale is 800 NN. (Figure 1) What is the reading in the right-hand scale?
T = 500 N
What relationship between the Sun and Earth did Copernicus formulate?
The Earth revolved in a circle about the Sun.
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.
A ship sailing from the ocean into a freshwater harbor sinks slightly deeper into the water. Does the buoyant force on the ship change? If so, does it increase or decrease?
The buoyant force does not change. The buoyant force on a floating object is always equal to that object's weight, no matter what the fluid.
What is the buoyant force that acts on a submerged object equal to?
The buoyant force is equal to the weight of the fluid displaced by the submerged object.
How does the buoyant force on a submerged object compare with the weight of the water displaced?
The buoyant force is equal to the weight of the water displaced.
If you were to expend 10 JJ of work to push a 1-CC charge against an electric field, what would be its change of voltage?
The change in voltage would be 10 V. 1 V is equal to 1 J / 1 C. 10 J / 1 C = 10 V
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.
How is the direction of an electric field defined?
The direction of the field is the direction of the force on a positive test charge
Remove the positive charge by dragging it back to the box at the bottom, and drag a negative charge (blue) toward the middle of the screen. Determine how the electric field is different from that of the positive charge. Which statement best describes the differences in the electric field due to a negative charge as compared to a positive charge?
The electric field changes direction (now points radially inward), but the electric field strength does not change. - The electric field is now directed toward the negative charge, but the field strength doesn't change. The electric field of a point charge is given by E⃗=(kQ/r2)r^E→=(kQ/r2)r^. Because of the sign of the charge, the field produced by a negative charge is directed opposite to that of a positive charge but the magnitude of the field is the same.
Which of the following describes the electric field produced by the positive charge?
The electric field is directed radially away from the charge at all locations near the charge.- This means that another positive charge, if placed near the original charge, would experience a force directed radially away from the original charge.
Now, remove the negative charge, and drag two positive charges, placing them 1 mm apart, as shown below. Let's look at the resulting electric field due to both charges. Recall that the electric field is a vector, so the net electric field is the vector sum of the electric fields due to each of the two charges. Where is the magnitude of the electric field roughly equal to zero (other than very far away from the charges)?
The electric field is roughly zero near the midpoint of the two charges. - Directly between the two charges, the electric fields produced by each charge are equal in magnitude and point in opposite directions, so the two vectors add up to zero.
As you stand on a floor, does the floor exert an upward force against your feet? How much force does it exert? Why are you not moved upward by this force?
The floor exerts a force on me, but I also exert a force on the floor. The net force between the floor and I is in equilibrium and that is why the floor does not move me up.
Suppose you increase the depth of the object WITHOUT changing its height. What will happen to the force due to pressure on the bottom of the object?
The force due to pressure on the bottom of the object will increase.
Suppose you increase the height of the object WITHOUT changing its depth under water. What will happen to the force due to pressure on the bottom of the object?
The force due to pressure on the bottom of the object will increase.
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.
Why do clothes often cling together after tumbling in a clothes dryer?
The increase in heat increases the charge of the clothes because it enables more electrons to transfer from the electrically charged metal of the dryer, to the clothes. Therefore the clothes are charged and are in turn drawn toward each other.
Why is it safe to remain inside a car during a lightning storm?
The metal in the frame of the car is a conductor so the charge will transfer from it to the ground and not inside to you. The car is also insulated which would further protect you from the charge.
Suppose you increase the height of the object WITHOUT changing its depth under water. What will happen to the net buoyant force?
The net buoyant force will increase.
Suppose you increase the depth of the object WITHOUT changing its height. What will happen to the net buoyant force?
The net buoyant force will stay the same.
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 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
What is the net force on an object in either static or dynamic equilibrium?
The net force is zero.
What is the condition in which the buoyant force on an object does equal the weight of the object?
The object is neutrally buoyant, so it will neither sink nor float.
What is probably being misunderstood by a person who says, "But that's only a scientific theory"?
The phrase the person meant to say was "but that's only a scientific hypothesis." Oftentimes people interchange the two words but they have completely separate meanings. Scientific theories are well-tested and are collections of verified hypotheses that lead to scientific understanding. Scientific hypotheses still need to be tested and experimented in order to prove them right/wrong. In this instance, the person is trying to discount an untested hypothesis; a scientific theory isn't "only" a theory due to the body of work that lead to the conclusions made within it, so this use of vocabulary is misinformed.
How does pressure at the bottom of a body of water relate to the weight of water above each square meter of the bottom surface?
The pressure is the weight of the water divided by 1 m2.
Why does the buoyant force act upward on an object submerged in water?
The pressure upward on the deeper bottom is greater than the downward pressure on the top.
When Dr. Hewitt immerses an object in water the second time and catches the water that is displaced by the object, how does the weight lost by the object compare to the weight of the water displaced?
The weight loss of the object is equal to the weight of the water displaced.
What are the circular spots of light seen on the ground beneath a tree on a sunny day?
These are pinhole images of the Sun.
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.
Some alphabet letters 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.
An energy of 0.10 J is stored in the metal sphere on top of a Van de Graaff generator. A spark carrying 1.0 micro-coulomb (1.0×10−6 C ) discharges the sphere. Find the sphere's potential relative to ground.
V = 1.0×10^5 V
Does the buoyant force on a submerged object depend on the volume of the object or on the weight of the object?
Volume
In lab you find that a 1-kg rock suspended above water weighs 10 N . When the rock is suspended beneath the surface of the water, the scale reads 8.0 N .If the container of water weighs 10 N on the weighing scale, what is the scale reading when the rock is suspended beneath the surface of the water?
W = 12 N
In lab you find that a 1-kg rock suspended above water weighs 10 N . When the rock is suspended beneath the surface of the water, the scale reads 8.0 N What is the scale reading when the rock is released and rests at the bottom of the container?
W = 20 N
Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 365 NN . What is Lucy's weight?
W = 730 N
In daily life, people are often praised for maintaining some particular point of view, for the "courage of their convictions." A change of mind is seen as a sign of weakness. How is this different in science?
When a scientist finds evidence that contradicts a law, then the law must be abandoned.
Compared with an empty ship, would a ship loaded with a cargo of Styrofoam sink deeper into the water or rise in the water? Defend your answer.
When a ship is empty its weight is least and it displaces the least water and floats highest. Carrying a load of anything increases its weight and makes it float lower. It will float as low carrying a few tons of Styrofoam as it will carrying the same number of tons of iron ore. So the ship floats lower in the water when loaded with Styrofoam than when empty. If the Styrofoam were outside the ship, below water line, then the ship would float higher as a person would with a life preserver.
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.
Why is blood pressure measured in the upper arm, at the elevation of your heart?
Your upper arm is at the same level as your heart, so the blood pressure in your upper arms will be the same as the blood pressure in your heart.
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.
Water pressure in a lake is greater __________.
at the bottom
Make an electric dipole by replacing one of the positive charges with a negative charge, so the final configuration looks like the figure shown below. The electric field at the midpoint is ________________.
directed to the right. - The electric field due to the positive charge is directed to the right, as is the electric field due to the negative charge. So the net electric field, which is the sum of these two fields, is also to the right.
The pressure increases on a block resting on a table when you increase the __________.
downward force on the block
The buoyant force on a floating object is __________.
equal to the object's weight
The magnitude of the electric field 1 mm away from the positive charge is ________________ the magnitude of the electric field 2 mm away.
four times - The magnitude of the field decreases more quickly than the inverse of the distance from the charge. The magnitude of the electric field is proportional to the inverse of the distance squared (E∝1/r2E∝1/r2, where rrr is the distance from the charge). You should verify this by looking at the field strength 3 or 4 meters away. This is consistent with Coulomb's law, which states that the magnitude of the force between two charged particles is F=kQ1Q2/r2F=kQ1Q2/r2.
On what factors does the buoyant force acting on an object depend?
height of the object
Rank the magnitudes of the net force on the block from most to least in the four situations, A, B, C, and D.
highest net force to loweset
A force of gravity pulls downward on a book on a table. What force prevents the book from accelerating downward?
support
A block of aluminum with a volume of 10 cm3 is placed in a beaker of water filled to the brim. Water overflows. The same is done in another beaker with a 10-cm3 block of lead. Does the lead displace more, less, or the same amount of water?
the same amount
Now, let's look at how the distance from the charge affects the magnitude of the electric field. Select Values on the menu, and then click and drag one of the yellow E-Field Sensors. You will see the magnitude of the electric field given in units of V/mV/m (volts per meter, which is the same as newtons per coulomb). Place the E-Field Sensor 1 mm away from the positive charge (1 mm is two bold grid lines away if going in a horizontal or vertical direction), and look at the resulting field strength. Consider the locations to the right, left, above, and below the positive charge, all 1 mm away. For these four locations, the magnitude of the electric field is________________.
the same. - This result implies that the strength of the electric field due to one point charge depends solely on the distance away from the charge. Mathematically, we say the electric field is spherically symmetric.
A scientific hypothesis deemed valid must have a test for proving it ______.
wrong
Find the voltage change when an electric field does 17 J of work on a 0.00005-C charge.
ΔV = 340 kV
Find the voltage change when the same electric field does 34 J of work on a 0.00010-C charge.
ΔV = 340 kV
State the equilibrium rule for forces in symbolic notation
ΣF = 0
