Walk on Water Notes Including Checks for Understanding

WOW Notes #1: DensityDensity = mass per unit volume

Typical metric units = or =

ρ

m

V

WOW Notes #1 CFU: Density1) What is the mass of 350 cm3 of H2O?

Answer: 350 g

2) What is the volume of 450 kg of H2O? Answer: 0.450 m3

3) ρAl = 2.64 = _______ Answer: 2640

4) What is the mass of 0.500 m3 of Aluminum? Answer: 1320 kg

WOW Notes #2: WeightWeight = the force of gravity, Fg

Fg = mg = Vρg

Units? x x = Newtons

WOW Notes #2 CFU: Weight5) What is the weight of 0.250 m3 of H2O?

Answer: 2450 N

6) What is the weight of 700. cm3 of Aluminum?

Answer: 18.1 N

WOW Notes #3: Other “density” valuesNote: Sometimes density is given in

weight/volume instead of mass/volume

values for water:8.33 or 62.4 or 2.20

ρg

Fg

V

WOW Notes #3 CFU: Other density values7. What is the weight in pounds of 50.0 gallons

of water? Answer: 417 lbs.

8. What is the volume in cubic feet of 150 pounds of water?

Answer: 2.4 cubic feet

9. What is the weight in pounds of the water contained in 13-2.0 Liter bottles of water?

Answer: 57 lbs.

WOW Notes #4: Archimedes and Buoyant ForceArchimedesWhen a solid object is immersed in a fluid it

displaces a volume of fluid equal to the volume of the solid.

WOW Notes #4 ContinuedArchimedes’ Principle: When an object is

immersed in a fluid, it experiences a buoyant force equal to the weight of displaced fluid.

WOW Notes #4 ContinuedApparent Weight = “true” weight– weight of displaced

fluid (buoyant force)

Fg´= Fg – Fb Fg´= Voρog – Vfρfgo = object and f = fluid

Also works with mass instead of weightThat is…apparent mass = “true” mass – mass of displaced

fluid (buoyant “force”)

WOW Notes #4 Continued

WOW Notes #4 CFU: Archimedes and Buoyant ForceWhat is the apparent weight of the aluminum

block pictured when it is immersed in water?Answer: 1.1 N

0.050 meters

0.045 meters

0.030 meters

Aluminum

WOW Notes #5: FloatingWhen an object FLOATS, the buoyant force

and the object’s weight are equal to each other…NO NET FORCE.

When an object is placed in a fluid it will either…Sink to the bottom because the weight of fluid

it displaces (buoyant force) is less than the weight of the object. (the net force is downward)

Sink into the fluid only to the point where it has displaced a volume of fluid equal to its weight. (the net force is zero)

WOW Notes #5 continued

WOW Notes #5 continued

WOW Notes #5 continued

WOW Notes #5 CFU: Floating1) Cannonball floating?2) Explain your observations of the cannonball

using the following vocabulary. (underline)1) Density, buoyant force, weight,

displace/displacement, net force, volume

WOW Notes #6: Stability and the Center of Buoyancy

WOW Notes #6: Stability and the Center of Buoyancy

WOW Notes #6: CFU

WOW Notes #7: Draft

WOW Notes #7: Draft

WOW Notes #7: DraftTo calculate “Draft” as a ratio:

Divide the volume of water necessary to displace by the volume of water that can be displaced.

Divide the weight you must support by the weight of water that can be displaced.

WOW Notes #7: CFU

WOW Notes #8: Acceleration!