Density Lesson for Absent Students
Read on page 11 about Physical properties of matter and examples.
Read about Density. Put definition for density in notebook.
Density is the amount of matter in a given space or volume.
D = m
V
D= density
m= mass
V= volume
Read about ping pong ball and golf ball.
We did the experiment with a ping pong ball and a golf ball.
Predict if the ball will sink or float based on past experiences.
Which one do you think is heavier? Does this affect whether it will sink or float?
We put both balls on the balance and got their mass in grams. The ping pong was 2.4 g and the golf ball was 45.6 g. Which one has more mass? Does that affect whether it sinks or floats? We dropped the golf ball in the water. It sank. We dropped the ping pong ball in the water. It floated. Then we took the balls out of the water. We decided to find their density. Remember density is mass divided by volume. We had already found the mass for each. Now we needed to find the volume. To do this we looked at the amount of water in the graduated cylinder. It was 1400ml. Then we dropped the golf ball in. It went up to 1420ml. So it displaced the water by 20ml. That was the golf ball’s volume.
Golf ball (mass) 45.6g = 2.28 g/ml (density)
(volume) 20ml
Then we put the ping pong ball in the water. The water level started at 1400ml. The golf ball floated so we had to push it down just under the water. The water rose to 1410. So the displacement of the water or volume was 10ml.
Ping pong ball 2.4g = .24 g/ml
10ml
Water has a density of 1. So, if the golf ball had a density of 2.28 it was greater than 1 then it would sink. The ping pong ball had a density of .24 which is less than 1 so it floated. The more dense an object the more likely it will sink. The less dense the object, then it is more likely to float.
Read in the book about the density of liquids. What liquid do you think is on the top? What floats on water? Read under the picture about what the different liquids are. What do you think would happen if you poured all of the liquids in at once? Do you think they would separate? Why or why not? Use the information in the book to help you.
Read about the density of solids. What do you think would be harder to carry, a kilogram of feathers or a kilogram of lead? Why? Do you remember when you were a little kid and people would ask, “Which one weighs more, a pound of feathers or a pound of bricks?” What is the answer? They both weigh a pound so they both weigh the same. Do you understand this section now?
In your notes put:
Water’s density is 1
Less than 1 = float
More than 1 = sink
Now read about different ways to measure density. Notice the different ways you can measure mass; grams (g) or kilograms (kg). Notice the different ways to measure volume; centimeters cubed (cm3) or meters cubed (m3) or milliliters (ml) or liters (L).
Solve for density on these examples: (use a calculator)
(Don’t forget, top number first then division symbol then bottom number equals)
25 g = g/cm3 Will this object sink or float? How do you know?
10cm3
45 kg = kg/m3 Will this object sink or float? How do you know?
43 m3
(Look at the unit of measure for both objects above. Which one is larger?)
20 g = (what’s the unit of measure)
49 ml Will this object sink or float? How do you know?
Then we tested Pepsi vs. Diet Pepsi. First we looked at the amount of liquid in each can. They both had 12 fl.oz. Then we put them on the balance and got the mass for the Pepsi. It was 387.6 g. The diet Pepsi had a mass of 370.4 Why do you think the regular Pepsi had more mass than the diet Pepsi? Do you think the different masses will affect whether or not they sink or float?
We put the Pepsi in the water and it sunk. When we put the diet Pepsi in the water, it floated. Then we decided to get the density of each. We took them out of the water. The container measured 1400ml of water. When we put the Pepsi in, it rose to 1800. What was the amount of displacement? Then we tested the diet Pepsi. It started at 1400. When we put the diet Pepsi in the water, it rose to 1800. So the displacement was the same, 400ml.
Solve for density for each:
Pepsi
387.6 g =
400 ml
Diet Pepsi
370.4 g =
400 ml
Why do you think if the densities were so close, did one sink and one float? Which one was closer to the density of water (1), Pepsi or diet Pepsi?