Wk 9 T2
What happens to particles when they are heated?
They move faster / gain kinetic energy.
Convection only occurs in these two states of matter.
Liquid and gases
What are the three methods of heat transfer?
Conduction, convection, and radiation.
What unit is used to measure energy?
Joules (J)
What type of energy does a moving car have?
Kinetic energy.
What is conduction?
This method of heat transfer occurs when heat moves through a solid by direct contact between particles.
What causes convection currents to form?
Differences in temperature and density
Why is plastic used for the handles of cooking utensils?
It is an insulator and reduces heat transfer to your hand.
What three variables are needed to calculate gravitational potential energy?
Mass, gravity, and height.
How does heat from the Sun reach Earth?
Radiation
What is the particle theory?
This theory states that all matter is made up of tiny particles that are constantly moving.
How do convection currents distribute heat in a swimming pool?
Warm water rises while cooler water sinks, creating a cycle that spreads heat.
Why are houses built with insulation in the walls and roofs?
To reduce heat transfer and maintain a comfortable temperature.
A 5 kg object is lifted 2 m. Calculate its GPE. (Use g = 9.8 N/kg)
GPE = m × g × h
= 5 × 9.8 × 2
= 98 J
A machine receives 1000 J of energy and produces 800 J of useful energy. What is its efficiency?
Efficiency = (Useful energy output ÷ Total energy input) × 100
= (800 ÷ 1000) × 100
= 80%
What is it was a poor insulator?
wood, rubber, glass, etc
How do ocean convection currents affect Earth's climate?
They redistribute heat around the planet.
Why is insulation important in buildings?
It reduces energy loss, lowers heating/cooling costs, and maintains temperature.
A 4 kg object is travelling at 5 m/s. Calculate its kinetic energy.
KE = ½ × 4 × 5²
= 2 × 25
= 50 J
Explain why metals conduct heat better than plastics using particle theory.
Metals have closely packed particles and free electrons that transfer energy quickly, while plastics transfer energy slowly.
What do free electrons do in metals?
Metals are usually good conductors because of these moving particles
Using particle theory, explain why warm water rises.
Heated particles move faster, spread further apart, making the water less dense so it rises.
A kettle uses 2000 J of energy but only 1500 J heats the water. What is the efficiency?
(1500 ÷ 2000) × 100 = 75%
A roller coaster has 1000 J of gravitational potential energy at the top of a hill. Ignoring friction, how much kinetic energy will it have at the bottom?
1000 J (energy is conserved).
A 3 kg ball travels at 10 m/s. Calculate its kinetic energy.
KE = ½ × 3 × 10² = 150 J