Download Inv 8

Name___________KEY_______________________________ Date_______10/31/14__________________
Investigation 8
Solids and Fluids
1.
What weighs more, one kilogram of lead or one kilogram of aluminum?
Same mass, same weight.
2.
What has more mass, a liter of ice or a liter of water? (1 liter = 1000 cm 3)
Ice is less dense than water. For the same volume, the water will have more mass.
3.
What has a greater density, one cubic centimeter of lead or ten cubic centimeters of aluminum?
Lead has a greater density than aluminum. Refer to density table.
4.
What has a greater density, five cubic centimeters of water or fifty cubic centimeters of water?
Same material, same density.
5.
Two dams are shown below – one with a large lake behind it and one with a small lake behind it.
Dam
A
a.
h
Dam
B
h
Which dam experiences a greater pressure on it due to the water at the same depth h? Explain.
Pressure depends on depth. At the same depth, the pressures are the same.
b.
Which dam experiences a greater force on it due to the water behind the dam? Explain.
Force is pressure x area. Since the pressures are the same, whichever dam has a larger area,
it will have the greater force.
6.
A rectangular block weighing 600 Newtons is resting on the floor.
It has a length, a width, and a height of 3 meters, 2 meters, and 1
meter, respectively. Find the pressure the block exerts on the floor
when the block rests on surface
a.
A.
pressure = force/area = 600/(1x3) = 200 N/m 2
b.
B.
pressure = 600/(1x2) = 300 N/m 2
c.
C.
pressure = 600/(2x3) = 100 N/m 2
2 meters
3 meters
C
1 meter
B
A
7.
A physics student is wading in a swimming pool. When she is in the water, she seems to weigh less
because of the buoyant force exerted on her by the water. Where does the buoyant force come from?
(That is, what’s responsible for the buoyant force?)
The upward pressure exerted by the water in the pool. The deeper you go, the greater the pressure.
8.
A physics student is in a boat that is floating in a lake. Inside the boat with the student is a block of
wood and block of steel.
The student throws the block of wood into the lake. She notices that the block of wood floats.
a.
What is the density of the wood in relationship to the density of water?
Wood is less dense than water.
b.
Will the boat now float higher or lower in the water than before the wood was thrown
overboard? Why?
The boat floats higher. It now weighs less.
c.
Will the water level of the lake go up, down, or remain at the same level? Think about whether
the block of wood displaces more water when it is in the floating boat or when it is floating in
the water outside the boat.
Water level will remain the same. The block of wood displaces the same amount of water
whether in the boat (floating) or outside the boat (floating).
The student now throws the block of steel into the lake. She notices that the block of steel sinks.
a.
What is the density of the steel in relationship to the density of water?
Steel has a density that is greater than water.
b.
Will the boat now float higher or lower in the water than before the steel was thrown
overboard? Why?
The boat floats higher. It now weighs less.
c.
Will the water level in the lake now go up, down, or remain at the same level? Think about
whether the block of steel displaces more water when it is in the floating boat or when it sinks
in the water outside the boat.
Water level goes down. The steel displaces more water when it is in the boat – an amount
equal to its weight. When thrown in the water, it displaces an amount of water equal to its
volume – not weight.
9.
Draw the height of the mercury columns in each
of the vertical tubes for the following
barometers. The atmospheric pressure
corresponds to normal atmospheric pressure at
sea level (76 cm of mercury).
76 cm of
mercury
mercury level in the
bowls
100 cm
80 cm
60 cm
40 cm
10. When you blow air over the top surface of a sheet of paper, the paper rises to a horizontal position.
Explain why. Don’t just say “Bernoulli’s Principle.”
air
high
velocity – low
low
pressure
velocity –
high
pressure
air
Do the next two experiments at home and report your results.
11. Place a few ice cubes in a glass of water. Carefully mark where the water level is on the glass. Cover
the glass to prevent any loss of water due to evaporation.
a.
Make a prediction as to the water level after the ice melts. Will the water level be higher, lower,
or remain the same?
b.
Wait until the ice cube is totally melted. Repeat the experiment to ensure that your
observations are accurate. Was your prediction correct? Explain why you got the results you
did.
Water level should remain the same. The ice cube displaces an amount of water equal to its
weight. But the ice is just water in a different form. So, the weight of the ice is the same as the
weight of the water it displaces – same weight, same volume.
12. Fill a glass to the top with water. Cover the glass with a card (e.g., a 3”x 5” card) so that it
completely covers the top of the glass. Hold the card onto the glass and invert the glass. (It might be
a good idea to do this over the sink.) Now release your hand. What happened? Why?
The water remained in the glass – the card stayed where it was. The card was held there by the
atmospheric pressure pushing upward on the card.