DENSITY And BUOYANCY

What is MASS? A measure of the amount of particles (matter) in an object. Matter= something that takes up space

Use a balance! Measured in grams It’s not weight How do you measure Mass? Use a balance! Measured in grams It’s not weight

What is Volume? The amount of space taken up by an object.

What do you use to measure Volume? Use a ruler or graduated cylinder Measured in cm3 or mL 1 cm3 = 1 mL

How do you measure Volume of a Regular Object? (If the object has straight sides like a cube) Measure the length of each side V = length x width x height

How do you measure Volume of an Irregular Object? (At least one side is not straight) Use displacement method. Put the object in a graduated cylinder. The volume of the object is the volume of the displaced fluid.

What is Spongebob’s Volume? 2 mL or 2 cm3

What is Density? The amount of mass per unit of volume. Depends on how tightly packed the particles are.

What is the rule for Density? less dense floats on more dense.

LESS DENSE MORE DENSE

What is the density of water? 1.0 g/mL

What is the density of water? Anything with a density greater than 1.0 g/mL will sink in water and anything with a density less than 1.0 g/mL will float in water.

Will lead sink or float in water if it has a density of 11.34 g/cm3 ?

Will ice sink or float in water if it has a density of 0.91 g/cm3 ?

How do you calculate density? To measure density, you must know the mass and the volume of an object. Density (g/cm3) = mass (g) volume (cm3) D = m/V Remember: density = love

m D v    v = volume m = mass D = density Welcome to the density triangle! It is just like the motion triangle, but with different values. m D v   v = volume m = mass  D = density

What are the steps to calculate density? 1. Circle the clue word. Determine what you are looking for. 2. Use the triangle to write the equation. 3. Plug in the data. 4. Calculate density,mass, or volume. Don’t forget units.

Density What is the density d = m/v g/cm3 g/mL Mass What is the mass Question Asks Equation Units Density What is the density d = m/v g/cm3 g/mL Mass What is the mass m = d x V g Volume What is the volume v = m/d cm3 mL

Example D = ?  looking for m = 5 g v = 30 mL 1. What is the density of a 5 gram sample that takes up 30 mL? D = ?  looking for m = 5 g v = 30 mL

m D v   

m D v 5 g    30 mL

5 g    30 mL

5 g    30 mL

Example solved D = m  v D = 5 g  30 mL Density = 5g/30mL = .16g/mL

Practice! 2. What is the density of an object with a mass of 3.0g and a volume of 5.0cm3?

Answer D = m/v m = 3.0g v = 5.0cm3 D = 3.0 g 5.0 cm3 D = 0.6 g/cm3

Practice! 3. What is the density of an object with a mass of 30.0 g and a volume of 10.0 mL?

Answer D = m/v m = 30.0g v = 10.0cm3 D = 30.0 g 10.0 cm3 D = 3 g/cm3

Practice! 4. What is the mass of an object with a volume of 5.0 cm3 and a density of 5.0 g/cm3?

Answer m = d x v d = 5.0 g/mL v = 5.0 mL m = 5.0 mL x 5.0 g/mL m = 25.0 g

Practice! 5. What is the volume of an object with a mass of 10.0g and a density of 2.0g/mL?

Answer V = m/d m = 10.0g d = 2.0 g/cm3 V = 10.0 g 2.0 g/cm3 V = 5 cm3

YOUR TURN!

What is the mass of an object with a volume of 1 What is the mass of an object with a volume of 1.0mL and a density of 5.0g/mL?

Practice! 5.0g/mL  1.0mL = 5g

Practice! What is the mass of an object with a volume of 10.0mL and a density of 2.0g/mL?

Practice! 2.0g/mL  10.0mL = 20g

Practice! What is the volume of an object with a density of 10.0g/cm3 and a mass of 2.0g?

Practice! 2.0g  10.0g/cm3 = 1 5 cm3

Let’s Practice What is the density of the following object: Mass = 5g Volume = 5mL 5g/5mL = 1 g/mL

Let’s Practice An object with a mass of 10g has a volume of 20mL. What is the density? 10g/20mL = .5g/mL

Let’s Practice A 20g object has a volume of 10mL. What is the density? 20g/10mL = 2g/mL

Let’s Practice A 50g object has a volume of 10mL. What is the density? 50g/10mL = 5 g/mL

Let’s Practice A 50mL object has a mass of 10g. What is the density? 10g/50mL = .2g/mL