Standard 8

All objects experience a buoyant force when immersed in a fluid.

Anticipatory Set

Why do you think these two liquids weigh differently when they are the same amount?

Standard 8.8 (a-b)

A. Students know density is mass per unit volume. B. Students know how to calculate the density of substances (regular and irregular solids and liquids) from measurements of mass and volume.

• LANGUAGE OF THE DISCIPLINE Density: the mass-to-volume ratio of a substance • Volume: is the amount of space occupied by a 3 D object • Graduated Cylinder: container used to measure volume of a liquid.

Density

•

Which grouping is the most dense below?

Density

• • Density is a physical property of matter Density can be used to identify things – Example: No matter what size Aluminum is, or what shape, it will always be the same density • The ratio of mass to volume will always be the same

Type of substance

Liquid Regular

Measuring Volume

Tool/method

Graduated cylinder Length * width * height Irregular solid Water displacement test V (solid)= V (water & solid) – V (water)

Water displacement

• • Example: What is the volume of the dinosaur?

V (solid)= V (water & solid) – V (water)

5.6

-

4.8

= 0.8

Calculating Density

Check for Understanding

• • • If you want to know the density and only know the mass what else do you need to find?

• volume What method should you use to find out the volume of an irregular solid?

• Water displacement How do you figure out the volume of a regular solid?

• Length x width x height

Practice & HW

• • •

Guided Practice:

– Read through Guided instruction on page 63-64 and highlight important information – Complete questions 1-4 on page 64 – Raise hand for a stamp

Independent Practice:

– Complete questions 1-4 on page 65

HW:

– Worksheet

Anticipatory Set

Why do some objects sink and some float?

Standard 8.8 (c-d)

C. Students know the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced. D. Students know how to predict whether an object will float or sink.

LANGUAGE OF THE DISCIPLINE • • • • Buoyant force: the upward force acting on a submerged object Hydrometer: tube-like instrument used to determine density of liquid compared to water Archimedes principal: a substance in a fluid is help up by a force equal to the weight of the displaced fluid Naturally buoyant: an object that will not sink

Buoyant Force

• • • is equal to the weight of the volume of fluid displaced by object.

–

So BIGGER VOLUME= BIGGER BUOYANT FORCE

Is measured in NEWTONS (since it is a force) This is why you feel lighter in water

Buoyant Force

• • Buoyant force occurs in fluids…

FLUIDS CAN BE GASES OR LIQUIDS

•

Example: Helium balloons rise because there is a greater buoyant force on it.

Archimedes’ principal

Pushed up by a force equal to weight of water displaced

Sink or Float

• Sinking and floating all has to do with density and buoyant force •

Naturally buoyant

objects will not sink • This is why oil floats on water- it is less dense!

Sink or Float

• EXCEPTION: sometimes very dense objects can float. – Example: Steel Boats – They can float because of they way they are shaped so they do not displace as much water. • Hydrometer – It will sink deeper in LESS dense liquid – Float higher in MORE dense liquid

Check for Understanding

Page 69- Questions 2-5

Answers: 2. The plate would sink 3. The weight of the rock is greater than the weight of the water displaced, so the rock will sink 4. The distance it sinks in hydrometer indicated the density. The lower it sinks the less dense the liquid 5. A beach ball on top of water (since the beach ball is full of a fluid- AIR)

Practice & HW

• • •

Guided Practice:

– Read through Guided instruction on page 67-69 and highlight important information – Complete the questions 6-8 on page 70 – Raise hand for a stamp

Independent Practice:

– Complete questions 1-4 on page 71

HW:

– worksheet.