"Archimedes' Principle" Buoyancy PPT Courseware 7

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"Archimedes' Principle" Buoyancy PPT Courseware 7

Archimedes' inspiration

More than two thousand years ago, the Greek scholar Archimedes wanted to measure the volume of a gold crown in order to determine whether it was pure gold. He thought hard for a long time but came up with no result. One day, when he stepped into a bathtub full of water to take a bath, he saw the water in the bathtub overflowing. He suddenly thought: Isn't the volume of an object immersed in liquid the same as the volume of liquid displaced by the object?

learning target

(1) Know Archimedes’ principle;

(2) Be able to find the magnitude of buoyancy;

1. The size of buoyancy

Think about it, do it

Press the can into a beaker filled with water and feel the relationship between buoyancy and the displaced liquid.

Volume of object immersed in liquid = volume of liquid displaced

Review: What factors are related to buoyancy?

The amount of buoyancy is related to the volume it is immersed in the liquid and the density of the liquid. The greater the volume immersed in the liquid and the greater the density of the liquid, the greater the buoyancy force.

Guess

The amount of buoyancy is related to the volume of liquid it displaces and the density of the liquid. The greater the volume of liquid displaced and the density of the liquid, the greater the buoyancy force.

How does buoyancy relate to displaced fluid?

How can the magnitude of buoyancy be expressed?

The buoyancy force may be related to the volume of liquid displaced x the density of the liquid

The amount of buoyancy may be related to the force of gravity displacing the liquid.

2. Archimedes’ Principle

Experiment to explore the relationship between the buoyancy force and the gravity of the displaced liquid

Fill in the recording form with measurement data;

Do several experiments with different objects and different liquids.

Analyze data to draw conclusions

1. An object immersed in a liquid experiences an upward buoyant force

2. The magnitude of the buoyant force is equal to the gravity of the liquid displaced by the object

1. Content: The buoyant force on an object immersed in a liquid is equal to the weight of the liquid it displaces.

2. Mathematical expression: F float = G row

3. Derived formula for calculation: F float = G row = m row g = r liquid gV row

4. Scope of application: liquids and gases

3. Discussion on Archimedes’ Principle

1. Distinguish between: immersion, immersion, immersion, immersion;

2. F float = r liquid gV discharge r liquid - the density of the liquid;

V row - the volume of liquid displaced by the object;

3. F float = r liquid gV discharge —— Determining formula

It shows that the size of buoyancy is only related to r liquid and V row.

The size of the buoyancy force has nothing to do with factors such as the shape and density of the object, the depth of immersion in the liquid, and whether the object moves in the liquid.

Example analysis

Example 1: The buoyancy force experienced by an object immersed in a liquid depends on ().

A. The volume of the object and the density of the liquid

B. The density of the object and the depth of the object immersed in the liquid

C. The volume of the object immersed in the liquid and the density of the liquid

D. Factors such as the mass, volume, depth and shape of the object immersed in the liquid

Example 2: An object with a volume of 300 cm3 floats on the water, and 2/3 of its volume is exposed out of the water. What is the buoyancy force it receives______N. (g is taken as 10 N/kg)

【Analysis】

According to Archimedes' principle:

F float = G discharge = ρ liquid gV discharge

According to the meaning of the question, row V=V/3

F float = ρ liquid gV discharge = 1.0×103 kg/m3×10 N/kg×10-4 m3=1 N

Example 3: If two solid iron balls and aluminum balls with the same weight are immersed in water, the buoyant force they experience will be ( ).

A. equal b. Aluminum balls are larger than iron balls

C. The aluminum ball is smaller than the iron ball D. Buoyancy is equal to gravity

【Analysis】

If the gravity of the iron ball and the aluminum ball are equal, then their masses are equal.

According to ρ=m/v, ρ iron > ρ aluminum, then V iron < V aluminum,

According to F float = ρ liquid gV discharge, ∴ F aluminum float > F iron float.

Summary of this lesson

What did you gain from studying this class?

1. Archimedes’ principle:

The buoyant force on an object immersed in a liquid is equal to the weight of the liquid it displaces.

2. Mathematical expressions:

F float = G row = m row g = r liquid gV row

Practice in class

1. The volume of the iron block is 100 cm3. When the iron block is completely immersed in water, the volume of water displaced is _____cm3, the weight of the water displaced is _____N, and the buoyancy force it receives is _____N. If it were completely immersed in alcohol, the buoyant force would be _____N. (g is taken as 10 N/kg)

2. When an object is hung under the spring dynamometer and immersed in water, the reading of the spring dynamometer is 1/3 of the reading of the spring dynamometer when the object is in the air. The density of this object is ( )

A. 1/3×103 kg/m3 B. 2/3×103 kg/m3

C. 3×103 kg/m3 D. 3/2×103 kg/m3

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Update Time: 2024-11-19

This template belongs to Physics courseware Lu Jiao Edition Eighth Grade Physics Volume 2 industry PPT template

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