3A5 Weight, Mass, and Density Flashcards
Explore the relationship between weight, density, and mass.
Define:
Mass
The amount of matter in an object.
Mass is constant regardless of location.
What are the common units of mass?
Some common units used are:
- Grams (g)
- Kilograms (kg)
- Pounds (lbs)
Mass can be measured in various units depending on the system used.
Define:
Weight
The downward force acting upon an object due to gravity.
Weight varies based on the strength of gravity at different locations. The equation is represented by W=mg, where m is equal to mass and g is equal to the force of gravity.
What is the difference between mass and weight?
- Mass is the amount of matter in an object.
- Weight is the gravitational force acting on that mass.
Mass is measured in kilograms (kg) and weight in newtons (N).
What misconception do people often have about weight and mass?
People often use “weight” and “mass” interchangeably, though they are distinct concepts.
Weight depends on gravity, while mass is intrinsic to the object.
True or false:
Mass remains constant, but weight changes depending on gravity.
True
Weight depends on the local gravitational acceleration (e.g., it’s lower on the Moon).
Fill in the blank:
Weight is a _____ quantity, while mass is a scalar quantity.
vector
Weight has both magnitude and direction, but mass only has magnitude.
Why is weight considered a force?
Because it is the result of gravitational acceleration acting on mass.
Weight follows F=mg,
where “F” is force (i.e., weight), “m” is mass and “g” is gravitational acceleration.
What is the SI unit of weight?
Newton (N)
Weight is a force.
Calculate the weight of a 10 kg object on Earth.
Weight = 10kg × 9.8m/s² = 98N
For this equation, use g = 9.8 m/s² to represent the acceleration due to gravity.
True or false:
An object’s mass changes if it’s taken to the Moon.
False
Mass remains constant regardless of location; only weight changes.
How can weight vary even if mass remains constant?
Weight changes due to variations in gravitational acceleration, such as on different planets.
g depends on the mass and radius of the celestial body.
How does weight vary on the Moon compared to Earth?
Weight on the Moon is approximately 1/6 of the weight on Earth due to weaker gravity.
The Moon’s gravitational acceleration is about 1.63m/s²
What happens to a person’s weight in outer space?
It becomes negligible because they are in free fall, experiencing microgravity, even though their mass remains unchanged.
Weight depends on gravitational force, which is much weaker in outer space.
True or false:
Weightlessness means the absence of mass.
False
Weightlessness occurs when there is no force supporting the object, but mass remains constant.
Why do astronauts experience weightlessness in space?
Because they are in free-fall along with their spacecraft, constantly falling towards Earth but never hitting it.
Weightlessness occurs when no normal force counters gravity, as in orbiting spacecraft.
Does weightlessness mean zero gravity?
No - gravity still acts, but there’s no support force to resist it.
Gravity is still acting on the object, but its effects are not felt due to free-fall conditions.
How does the weight of an object vary at the poles and the equator?
Weight is slightly higher at the poles due to stronger gravitational acceleration.
Earth’s shape causes gravity to be weaker at the equator.
Why do objects weigh less at higher altitudes?
Gravitational acceleration decreases as the distance from Earth’s center increases.
The effect is negligible for most everyday altitudes but noticeable on mountains.
Fill in the blank:
On Jupiter, a person’s weight would ______ compared to Earth
increase
Jupiter’s stronger gravity increases the weight of the same mass.
Give an example of how weight is used in designing safety equipment.
Parachutes are designed to counteract weight with air resistance for safe descent.
Understanding weight helps optimize safety designs and material strength. Weight affects helmets, airbags, and parachutes to reduce impact forces.
What happens to an object’s weight when submerged in water?
The apparent weight decreases due to the buoyant force of the displaced water.
Weight measured underwater is less than actual weight in air.
What device is used to measure mass rather than weight?
A balance or beam scale.
Balances compare masses directly, independent of gravitational variations.
How does a scale measure weight?
A scale measures the gravitational force acting on an object and converts it into a weight reading.
Digital and mechanical scales use different mechanisms but rely on W=mg.
How do spring scales work to measure weight?
They measure the extension of a spring proportional to the gravitational force acting on the object.
Hooke’s Law is applied: F=kx.
Define:
Density
Measure of how much mass is contained in a given volume, calculated as mass divided by volume (𝜌=M/v)
Density helps compare how compact different substances are.
Define:
Volume
Amount of three-dimensional space occupied by an object or substance, measured in units like cubic meters (m³), liters (L), or milliliters (mL).
Volume can be calculated differently depending on the object’s shape, e.g., using geometry for regular shapes or displacement methods for irregular ones.
What are the common units of density?
Kilograms per cubic meter (kg/m³) in the SI system and grams per cubic centimeter (g/cm³) in the CGS system.
For liquids, density is often expressed in g/mL or kg/L.
True or false:
Objects with the same mass always have the same density.
False
Density depends on both mass and volume.
Calculate the density of an object with a mass of 200g and a volume of 50cm³.
Density = 200g/50cm³ = 4g/cm³
Ensure units are consistent when calculating density.
What happens to the density of an object if its volume decreases but mass remains constant?
Density increases.
Density is inversely proportional to volume.
Fill in the blank:
Less dense objects ______ in a denser fluid.
float
Buoyancy depends on relative densities of the object and the fluid.
Define:
Buoyant force
The upward force exerted by a fluid on a submerged or floating object.
The magnitude of buoyant force equals the weight of the fluid displaced by the object.
How does the buoyant force depend on the density of the fluid?
Higher fluid density results in a greater buoyant force.
Buoyant force is expressed as Fb=𝜌𝑉g, where 𝜌 is the fluid density, V is displaced volume, and g is gravity.
True or false:
The buoyant force always acts upward.
True
Buoyant force counteracts gravity and acts perpendicular to the fluid’s surface.
What happens to the buoyant force when an object is fully submerged compared to partially submerged?
The buoyant force is greater when the object is fully submerged.
Fully submerged objects displace a larger volume of fluid.
How does Archimedes’ principle apply to ship design?
Ships are designed to displace water equal to their weight, ensuring they float.
The upward buoyant force must balance the ship’s weight to stay afloat.
How does the principle of buoyancy apply to submarines?
Submarines adjust their buoyancy by controlling the amount of water in ballast tanks to sink or rise.
This is achieved by changing the overall density of the submarine.
Why do icebergs float on water?
Ice is less dense than water, so it displaces enough water to equal its weight before fully submerging.
Approximately 90% of an iceberg is submerged.
How does Archimedes’ principle explain the working of a hydrometer?
A hydrometer floats at different levels depending on the liquid’s density.
The depth of immersion changes with the liquid’s buoyant force.
Why do life jackets help people stay afloat?
They increase the wearer’s overall volume, decreasing density and increasing buoyancy.
The displaced water’s buoyant force supports the person’s weight.
How is Archimedes’ principle used in metal purity testing?
By measuring the volume of water displaced, the density of the metal can be calculated to check purity.
This method is often used to test gold and other precious metals.
True or false:
A steel ship floats because it has a lower density than water.
True
The overall density of the ship (including air inside) is less than water.
Why do helium balloons rise in air?
Because helium has a lower density than air.
Buoyant force exceeds the balloon’s weight.
True or false:
A denser object will always sink in water.
False
If the object’s shape increases its volume enough, it can still float (e.g., ships).
Compare the density of a liquid and a solid with the same mass but different volumes.
The solid has higher density due to its smaller volume.
Density increases as volume decreases for constant mass.
Why is density an important property in material selection?
It determines the material’s suitability for applications like buoyancy, construction, or strength.
High-density materials are often used for strength, while low-density materials are used for lightness.
Why does a hot air balloon rise?
The heated air inside the balloon is less dense than the cooler surrounding air, creating buoyancy.
The buoyant force exceeds the weight of the balloon.
What happens if an object’s density equals the density of the fluid it’s in?
The object remains suspended at the same level in the fluid.
The forces of gravity and buoyancy balance each other.
True or false:
Weight is only dependent on the object’s density and not its volume.
False
Weight depends on both the object’s density and volume, as Weight = Density × Volume × g.
Fill in the blank:
Objects with higher ______ generally weigh more for the same volume.
density
Weight is directly proportional to density for a given volume, as Weight=Density×Volume×g.
How does the density of a material affect the design of weighing scales?
Scales must account for density to ensure the material’s weight corresponds to its mass accurately, especially in fluids or uneven terrains.
Buoyant forces acting on less dense materials can affect readings, requiring calibration.
Why do denser objects sink while less dense objects float in a liquid?
Denser objects sink because they cannot displace enough liquid to counteract their weight.
The buoyant force depends on the liquid’s density and the displaced volume of the object.
Fill in the blank:
A ______ is commonly used to measure the density of liquids by floating in them.
hydrometer
A hydrometer determines liquid density based on the buoyant force exerted on it.
True or false:
A pycnometer can measure the density of both solids and liquids.
True
A pycnometer calculates density by comparing the mass of a known volume of the material with that of a reference liquid.
How does a digital density meter measure density?
It uses the oscillation principle to calculate density with high precision.
The device measures the change in oscillation frequency caused by the sample’s mass in a vibrating tube.
