One big idea
A principle helps us make sense of many situations.
The ball in the bowl
A ball is released from the left edge of a smooth bowl and rolls down and up the other side.
How high will it climb on the right?
What this lesson covers
The idea
Principles are broad ideas that help us make sense of a given situation.
The ball in the bowl
A ball is released from the left edge of a smooth bowl and rolls down and up the other side.
How high will it climb on the right?
- Higher than the start
- About the same height as the start
- Much lower than the start
Slide the ball
Drag the ball along the track. Watch the height energy and motion energy bars.
The same idea everywhere
Principles are broad ideas that help us make sense of a given situation.
Here the idea is the principle of conservation of energy: energy changes form, but the total stays the same. Height energy turns into motion energy, and back again.
One broad idea makes sense of many different situations. That is what a principle does.
- Situation | Energy changes
- Ball in a bowl | height energy ↔ motion energy
- Climbing stairs | energy from food → height energy (and some warmth)
- Kicked football going up | motion energy → height energy
Notes
Principles are broad ideas that help us make sense of a given situation, like conservation of energy: energy changes form, but the total stays the same.
Check yourself
What is a scientific principle?
In the bowl the total is 2 units. At one spot the ball has 0.5 units of height energy. How many units of motion energy does it have?
Answer: 1.5 units
Motion energy = 2 − 0.5 = 1.5 units. The total stays 2.
Climbing the stairs shows the principle of conservation of energy. What does it say about the energy you get from food?
The ball reaches the same height on the other side. Which broad idea explains this?
- A broad idea that helps us make sense of a situation — correct. Yes. For example, conservation of energy.
- A rule made by the school. Principles come from nature, not from schools.
- A single measurement. A principle is a broad idea, not one number.
- It disappears as you climb. The principle says energy is not destroyed.
- It changes into other forms, such as height energy, and the total is kept — correct. Yes. Energy changes form, but the total stays the same.
- It is created again as you climb. Energy is not created either.
- Conservation of energy: height energy and motion energy swap, and the total stays — correct. Yes. With no friction, the total never changes.
- Balls always want to go up. Balls do not want anything. Energy explains it.
- The bowl pushes the ball up. The bowl is not adding energy.