Heat Transfer
Which method of thermal energy transfer requires direct contact between objects?
Conduction
State Newton's First Law of Motion in one sentence (use grade-appropriate language).
An object at rest stays at rest and an object in motion stays in motion at constant velocity unless acted on by an unbalanced force.
Which term includes direction: speed or velocity?
Velocity includes direction.
Write the formula for average speed using distance and time. (Use symbols if helpful.)
Formula: average speed = total distance ÷ total time (v_avg = distance / time).
What is the total distance traveled?
80 km
Name the thermal energy transfer that occurs when warm fluid rises and cooler fluid sinks, forming a cycle.
Convection.
If a soccer ball is rolling at constant speed across a field with no friction, what net force acts on it? (Balanced or unbalanced?)
Balanced (net force = zero) — no net force if speed is constant and no friction.
A car travels 30 kilometers east in 0.5 hours. Is the value 60 km/h a speed or a velocity? Explain why.
It's a velocity if direction "east" is included; 60 km/h east would be a velocity; 60 km/h without direction is speed.
A bicycle travels 15 kilometers in 0.5 hours. Calculate the average speed in km/h. Show your work.
Average speed = 15÷0.5=30 km/h15÷0.5=30 km/h.
What is the speed from point A to B?
2 km/ min
Give an everyday example of radiation (thermal energy transfer) that students can observe outdoors.
Example: Feeling warmth from the sun (infrared radiation) or heat from a campfire without touching flames.
Describe what will happen to a book resting on a table if the table is suddenly removed (briefly explain using Newton's First Law)
The book will fall (accelerate downward) because when the table is removed, the upward support force is gone and gravity (an unbalanced force) causes motion.
Define displacement and explain how it is different from distance (use a short example)
Displacement is straight-line distance from start to finish with direction (vector); distance is total path traveled (scalar). Example: Walking 3 m east then 4 m west: distance = 7 m, displacement = 1 m west.
During an investigation, a toy car travels 2.4 meters in 3 seconds. Calculate the average speed in m/s.
Average speed = 2.4÷3=0.8 m/s2.4÷3=0.8 m/s.
What is the average speed?
1.6 km/ min
Explain why a metal spoon in a hot pot becomes hot faster than a wooden spoon in the same pot. (Name the property of metal that makes this happen.)
Metals conduct heat well (high thermal conductivity); wood is an insulator.
A skateboarder is moving and suddenly hits a patch of rough gravel; the skateboard stops but the rider continues forward. Explain this using Newton's First Law.
The skateboard stops due to an unbalanced force (friction) acting on the skateboard; the rider continues forward due to inertia.
Two runners each run 400 m around a circular track and end at the starting point. Which quantity is zero for each runner: distance, displacement, or velocity? Explain.
Distance = 400 m for each runner; displacement = 0 m (they returned to start); average velocity over the trip = 0 m/s (because displacement over total time is zero) while speed is not zero.
A student performs two trials: Trial A distance = 50 m, time = 10 s; Trial B distance = 50 m, time = 8 s. Which trial had the greater average speed and what are the speeds?
Trial A: 50÷10=5 m/s50÷10=5 m/s. Trial B: 50÷8=6.25 m/s50÷8=6.25 m/s. Trial B had greater average speed.
What is the object doing from B to C?
Return to start
Describe how all three methods of thermal energy transfer (conduction, convection, radiation) can be involved when heating water in a pot on a stove.
Stove burner heats pot by conduction; water at bottom heats, becomes less dense and rises (convection); the burner and hot surfaces also emit infrared radiation that warms nearby objects.
Provide a real-life scenario where balanced forces act on a moving object so it continues at constant velocity, and explain why the forces are balanced.
Example: A car cruising at constant speed on a level road with cruise control where engine thrust balances air resistance and friction; net force ≈ zero so velocity stays constant.
A student walks 10 m north, then 6 m south. Calculate the total distance and the displacement (give direction for displacement).
Calculating Average Speed
A hiker walks 4.2 km in 1.5 hours, then rests, then walks another 2.8 km in 0.7 hours. Calculate the overall average speed for the entire trip (total distance divided by total time). Show steps.
Total distance = 4.2+2.8=7.0 km4.2+2.8=7.0 km. Total time = 1.5+0.7=2.2 hours1.5+0.7=2.2 hours. Overall average speed = 7.0÷2.2≈3.18 km/h7.0÷2.2≈3.18 km/h.
What does a flat line mean?