Energy Transfers
What type of energy transfer happens when you feel the warmth of the sun on your face?
Radiation
What is the unit for energy?
On a heating curve, what happens to temperature during a phase change?
What happens to the kinetic energy of particles when a substance is heated?
Why does metal feel colder than wood when you touch both at the same temperature?
Because metal conducts heat away from your hand faster than wood.
Which type of energy transfer happens in liquids and gases when hot particles move and transfer heat to cooler particles?
Convection
A 2 kg object is raised to a height of 10 meters. How much potential energy does it have?
Ep = mgh = 2 x 10 x 10 = 200 J
Why is there a flat section on a heating or cooling curve?
Because energy is being used for a change of state, not temperature increase.
When you heat a solid, how do the particles move?
They vibrate faster
Why does your sweat cool you down when it evaporates?
Because the evaporation of sweat absorbs heat from your body (latent heat of vaporisation).
What type of energy transfer occurs when a metal spoon heats up in a cup of hot tea?
Conduction
A 5 kg object is moving at a velocity of 10 m/s. What is its kinetic energy?
Ek=1/2(5)(10^2)= 250 J
On a cooling curve for water, what change of state happens at 0°C?
Freezing (liquid to solid)
What do we call the things that hold particles together in a solid and liquid
Bonds or forces of attraction
Why do you feel cold when you get out of a swimming pool, even on a warm day?
Because water evaporates from your skin, taking heat away from your body (latent heat of vaporisation).
How does convection work in liquids and gases? Why do hot fluids rise and cool fluids sink?
Convection occurs because of differences in density. When a fluid is heated, its particles move faster, causing the fluid to expand and become less dense. The less dense (hot) fluid rises, while the denser (cool) fluid sinks, creating a convection current. This is how heat is transferred in fluids.
Rearrange the equation for kinetic energy to solve for velocity (v) and include unit.
v = square root (2Ek/m) in m/s
During the boiling point phase, what type of energy is being added without increasing temperature? (HINT: answer is 4 words)
Latent heat of vaporisation.
In terms of particle behavior, why does a solid melt into a liquid when heated?
The particles gain enough energy to overcome some of their attractions and move around each other.
Why does a hot air balloon rise?
The air inside the balloon is heated, expanding and becoming less dense than the cooler air outside, causing the balloon to rise.
Name three features of a thermos that help keep liquids warm, and explain what type of energy transfer each feature stops.
Vacuum between the inner and outer walls: Stops convection and conduction because there’s no air for heat to travel through.
Reflective surface inside the thermos: Stops radiation by reflecting heat back into the liquid.
Cork or plastic stopper: Helps prevent convection (stopping hot air from escaping or cool air from entering).
A 2 kg object is dropped from a height of 25 meters. What is its speed just before hitting the ground, assuming no air resistance?
Ep = mgh = 2 x 10 x 25 = 490 J
Ep = Ek = 1/2 mv^2 (rearrange for v) = 22.14 m/s
Describe the particle behavior during the flat section of the cooling curve when gas condenses into liquid.
Particles lose kinetic energy and move closer together to form a liquid.
Explain why gases have much lower densities than solids or liquids, using kinetic particle theory.
Gas particles move freely and are far apart because of their high kinetic energy.
If you are boiling water to make pasta, why do you need to keep adding heat to maintain boiling even though the water’s temperature is 100°C?
The added heat is being used to convert the liquid water to steam (latent heat of vaporisation).