Uploaded by Shahriar Turja

Floating and Sinking

Worksheet/Information Sheet
Worksheet/Information Sheet No:
Student’s Name
Subject : Physics
Teacher’s Name
:Shahriar Turja
: O Level
: Floating and Sinking
Density: The compactness and size of the molecules or particles of a substance
the more compact or squished together the molecules are and the
more mass the particles have, the larger the density
Density is a characteristic property of substances and can be used to
help identify substances.
MASS: is the amount of matter an object contains
Mass does not change unless you add or remove matter
VOLUME: is the amount of space an object occupies
Density = Mass / Volume
Finding Mass and Volume
Mass is always determined using a balance.
Triple beam or electronic
Remember you always must take into account the mass of the container one of
two ways:
Tare the balance (zero out the container’s mass)
Or measuring the mass of the container and then subtracting it out later
from the total mass of the container + substance
Volume can be found in different ways, depending on the substance or object.
Liquid volumes are read in volumetric lab equipment, like a graduated cylinder or
The dimensions of regularly shaped objects may be measured and then the
volume found by using a formula such as V=l x w x h.
The volume of irregularly shaped objects may be found by water displacement
• measure a given amount of water in a graduated cylinder
• add the object and read the volume of the water + object
• then find the volume of the object by subtraction.
Amount of H2O with object = ______
About of H2O without object = ______
Difference = Volume = ______
Mass units are usually grams (g)
Volume units are usually
Milliliters (mL) or cubic centimeters (cm3) for liquids or solids
1mL = 1cm3
L for gases
Density units will always be a (Mass unit/ volume unit) like g/mL or g/cm3 or g/L.
Using the density formula
D=m/v can be used to solve for density if the mass and volume is known
What if the density is known, and you need to find the mass or volume?
Just rearrange the formula to solve for the unknown: m=D*v
or v=m/D
Upthrust: When a body is partially or wholly immersed in a liquid, and upward force
acts on it known as upthrust. Upthrust is a force, it is measured in Newton (N).
The Effect of upthrust: Its effect is that weight of the body immersed is liquid appears
to be less than its actual weight.
Plimsoll line: The Plimsoll line is a reference mark located on a ship’s hull that indicates
the maximum depth to which the vessel may be safely immersed when loaded with
cargo. This depth varies with a ship’s dimensions, type of cargo, time of year, and the
water densities encountered in port and at sea. Once these factors have been
accounted for, a ship’s captain can determine the appropriate Plimsoll line needed for
the voyage
Hydrometer: A hydrometer is an instrument to measure the relative density of liquids.
It consists of a tube with a bulb at one end. Lead shots are placed in the bulb to weigh it
down and enable the hydrometer to float vertically in the liquid.
In a liquid of lesser density, a greater volume of liquid must be displaced for the buoyant
force to equal to the weight of the hydrometer so it sinks lower.
Hydrometer floats higher in a liquid of higher density.
Application of Archimedes’ Principle
1. Submarine:
A submarine has a large ballast tank, which is used to control its position and depth
from the surface of the sea. A submarine submerges by letting water into the ballast
tank so that its weight becomes greater than the buoyant force.
Conversely, it floats by reducing water in the ballast tank. -thus its weight is less than
the upthrust (buoyant force).
2. Hot-air balloon
The atmosphere is filled with air that exerts buoyant force on any object. A hot air
balloon rises and floats due to the buoyant force (when the surrounding air is greater
than its weight). It descends when the balloon’s weight is higher than the buoyant force.
It becomes stationary when the weight equals the buoyant force.
The weight of the Hot-air balloon can be controlled by varying the quantity
of hot air in the balloon.
3. Ship
A ship floats on the surface of the sea because the volume of water displaced by the
ship is enough to have a weight equal to the weight of the ship.
A ship is constructed in a way so that the shape is hollow, to make the overall density of
the ship lesser than the sea water. Therefore, the buoyant force acting on the ship is
large enough to support its weight.
The density of sea water varies with location. The PLIMSOLL LINE marked on the body
of the ship acts as a guideline to ensure that the ship is loaded within the safety limit.
A ship submerge lower in fresh water as fresh water density is lesser than sea water.
Ships will float higher in cold water as cold water has a relatively higher density than
warm water.
Certain group of fishes uses Archimedes’ principles to go up and down the water.
To go up to the surface, the fishes will fill its swim bladder (air sacs) with gases (clever
isn’t it?).
The gases diffuse from its own body to the bladder and thus making its body lighter.
This enables the fishes to go up.
To go down, the fishes will empty their bladder, this increases its density and therefore
the fish will sink.