Vocabulary & Definitions
What is density?
The mass per volume.
A metal block and a wooden block have the same volume. The metal sinks in water, but the wood floats. Why?
Metal has more mass and higher density than water, so it sinks. Wood has lower density than water, so it floats.
A steel cube sinks in water, but a large steel ship floats. How is this possible?
The ship's overall volume is larger compared to it's mass, so it's density is less than water, allowing it to float.
A balloon is placed in hot water and inflates. Explain using particle movement.
Heating increases particle speed: they spread apart, increasing the gas volume inside the balloon.
Oil has a lower density than water.
What is volume?
How would you measure the volume of an irregularly shaped object if you do not have a ruler?
Why do liquids of different densities form layers when mixed in a container?
Denser liquids sink to the bottom and less dense liquids float on top to reach equilibrium.
How do the particles move in the different states of matter?
Gas: move around
Liquid: move slightly
Solid: shake
How can submarines sink or rise in the ocean without changing shape?
They adjust their overall density by filling ballast tanks with water (sink) or air (rise).
What is buoyancy?
The upward force exerted by a fluid on an object.
A student measures the mass of an object as 50 g on Earth. What would the mass be on the Moon? Explain.
Mass would still be 50 g because mass does not depend on location.
A helium balloon rises in air. Is it's density greater than, less than, or equal to air? Explain.
Less than air: the buoyant force is stronger than the weight of the balloon.
How does particle movement in gasses change when pressure is applied?
Faster-moving particles collide more often and with greater force.
Ice floats on water even though it is solid. What does this tell you about ice compared to liquid water?
Ice is less dense than liquid water, which is why it floats.
What is pressure?
The force on units per area.
If two objects have the same mass but different volumes, which one is denser? Explain.
The object with smaller volume is denser because density = mass/volume.
How does Archimedes' Principle explain why objects feel lighter in water?
The upward buoyant force equals the weight of the displaced water, reducing the objects apparent weight.
What happens to density when a solid melts into a liquid?
Usually decreases (particles spread out), except water.
A hot air balloon floats because the air inside is less dense than the surrounding air. How could you make it rise faster?
Heat the air inside the balloon to make it less dense, increasing buoyant force.
Matter is made of tiny particles that are always moving, and the way they move and how close together they are determines whether something is a solid, liquid, or gas.
What is the formula to calculate density?
Density = mass/volume
What happens to density if mass increases but volume stays the same?
Density increases.
Higher temperature is faster particles is more collisions is higher pressure. Lower temperature is slower particles is lower pressure.
Why does a soda can explode when left in heat?
Heat increases pressure inside because gas particles move faster and push on the can walls.