• In S415 ESC

• Can be done anytime during week

• Turn into boxes outside classroom.

• No make-up--equipment is taken down Sat.

Labs

A cube under water

Buoyant Force:

The force caused by the difference in pressure between the top and the bottom of an object when the object is in a fluid (liquid or gas).

The buoyant force on an object totally submerged in a fluid depends on

a)The mass of the objectb)The volume of the object,

or c) Both.

A cube floating on water

What if it’s not a cube?

Eureka!

Archimedes principle: The buoyant force is always the weight of the fluid that the object is displacing at the moment.

Consider a rowboat floating on a lake. The weight of the rowboat, including the people sitting in it, is 500 pounds. The buoyant force on the rowboat is a) Greater than 500 pounds,b) Less than 500 pounds, orc) Equal to 500 pounds.

Three cubes of the same size are completely submerged under water: lead, steel and wood. The bouyant force is greatest on the _______ cube

1. Lead2. Steel3. Wood4. None… it is the same

Three Cases1) Penny— More dense than the liquid2)Ping Pong Ball— Less dense than the liquid3) Submarine, fish – Neutral buoyancy

Submarines and fish can adjust their

density!

A cannon is placed in a boat. The boat sinks a little to displace more water.

The amount of new water displaced is

1. A volume of water that weighs more than the cannon.

2. A volume of water that weighs as much as the cannon.

3. A volume of water that weighs less than the cannon.

If the cannon now falls from the boat into the water and sits on the bottom

of the lake the amount of water displaced by the cannon is

1. A volume of water that weighs more than the cannon.

2. A volume of water that weighs as much as the cannon.

3. A volume of water that weighs less than the cannon.

Discussion question: A glass is filled to the top with ice and water. When the ice melts, where is the water level?

1. Above the rim so it spills over.2. At the rim—same place as

before.3. Below the rim

A container of water is sitting on a scale. I dip my finger into the water without touching the sides or the bottom of the container. The normal force exerted on the scale willa) Increase,b) Decrease, orc) Remain the same

An object is hanging on the end of a string and is submerged in water. The tension in the string is

a) Less than,b) Greater than, orc) Equal to

the weight of the object.

Discussion Question: An Alka-Seltzer tablet dissolves in water and the CO2

gas goes into a balloon. When it dissolves the scale reading

1. Goes up2. Goes down3. Stays the same