Knives are considered sharp when

1. The blade is shiny

2. The force gets larger

3. The pressure gets smaller

4. The blade gets thinner

5. They plunge into your heart

Knives are considered sharp when

1. The blade is shiny

2. The force gets larger

3. The pressure gets smaller

4. The blade gets thinner

5. They plunge into your heart

P F

A

If the area is smaller the pressure is larger due to P and A being inversely proportional

This question allows me to test on their ability to understand not only the inverse relationship between the force and area, but also probes them to understand what is changing.

What are the units of pressure?

A. Newtons per square meter

B. Pascals

C. Pounds per square inch

D. All of the above

What are the units of pressure?

A. Newtons per square meter

B. Pascals

C. Pounds per square inch

D. All of the above

I use this as a clicker question so they see that there are many different ways to indicate the units of pressure. This is used either as a pre-reading question, or review at the beginning of lecture.

What has the larger buoyant force when placed in a chocolate shake?

• A. Aluminum• B. Lead• C. Same• D. Need to know density of the liquid

The metal blocks are the same volume

What has the larger buoyant force when placed in ANY liquid?

• A. Aluminum• B. Lead• C. Same• D. Need to know density of the liquid

The metal blocks are the same volume so each displaces the same amount of syrup. The buoyant force equals the weight of the displaced liquid.

This question starts a series of 4 questions focusing on the different ways to conceptualize the buoyant force. It is an application of the definition of buoyant force.

Buoyant ForceArchimedes Principle

• The buoyant force is equal to the weight of the displaced fluid

• The more volume displaced, the larger the force

Salt water is slightly denser than fresh water. A 50-ton ship will experience a greater buoyant force floating in a lake of…

A. salt water

B. fresh water

C. The buoyant force is the same in either lake

Salt water is slightly denser than fresh water. A 50-ton ship will experience a greater buoyant force floating in a lake of

A. salt water

B. fresh water

C. The buoyant force is the same in either lake

Since the boat floats the upward buoyant force is equal to the downward weight

Fg

FB

This is a question that a majority of students answer incorrectly. It should focus on the use of Newton’s but students focus on the differences in density.

Salt water is slightly denser than fresh water. An underwater submarine will experience a greater buoyant force in

A. salt water ocean

B. fresh water lake

C. The buoyant force is the same in either lake

Salt water is slightly denser than fresh water. An underwater submarine will experience a greater buoyant force in

A. salt water ocean

B. fresh water lake

C. The buoyant force is the same in either lake

Since more mass is displaced in salt water the buoyant force will be larger.

This is a follow-up that I use to show them how to appropriately apply buoyancy to submerged objects

Salt water is slightly denser than fresh water. A 50-ton ship will displace more water in the

A. salt water lake

B. fresh water lake

C. the same in either lake

Salt water is slightly denser than fresh water. A 50-ton ship will displace more water in the

A. salt water lake

B. fresh water lake

C. the same in either lake

DMV

V fresh MD fresh

This question also follows up the ship problem, but instead of asking about force, which is the same for a ship in fresh or salt water, it asks about the volume of water displaced. Hopefully they can make the distinction.

A 500-g wooden block is lowered carefully into a completely full beaker of water and floats. The weight of the water, in newtons, that spills out of the beaker is about?

A. 0.5 N

B. 5 N

C. 10 N

D. 15 N

A 500-g wooden block is lowered carefully into a completely full beaker of water and floats. The weight of the water, in newtons, that spills out of the beaker is about?

A. 0.5 N

B. 5 N

C. 10 N

D. 15 N

W Fg mag 0.5kg 10m

s2

5N

The buoyant force is equal to the weight of the displaced fluid. I use this question to bring the lecture back to the main point.