Natural Science
Computer Science

 A ball rolls down a hill. Where does it roll the fastest?

At the bottom of the hill. Gravity causes the ball to speed up--accelerate--as it rolls down the hill. It keeps accelerating until its speed maxes out at the bottom of the hill


Is global warming real? Is it a problem? What is it?

Global warming is a real and serious problem. There are many causes of global warming, such as harmful chemicals in the atmosphere from pollution, deforestation, and even cow farts! It's important that we all do our part to help slow down global warming, like using less water, eating more plants, and turning the lights off when we leave the room.

Are computers smarter than people?

Computers are not smarter than people. Computers are actually not smart at all! They need very specific instructions in order to carry out simple tasks. This is why you need to know exactly what you want the computer to do when you code something.


Choose any number and subtract it from itself. What do you get?

0. 1-1=0, 2-2=0, 3-3=0, and so on. This is called an identity and it allows mathematicians to solve things in general, using letters or symbols instead of just numbers.


Why is it harder to slide on wood than on ice?

Friction. Ice has less friction than wood and therefore lets things slide with less effort on its surface. Friction is a force that opposes motion of an object across a surface.


What is an eclipse and why is it rare?

An eclipse happens when the moon blocks sun from our view. The moon rotates around the spinning earth which rotates around the sun. Eclipses are rare since the rotation cycles of the sun moon and earth need to line up perfectly so that the moon blocks the sun from earth


Suppose you wanted to animate a creeper moving from left to right across the screen. The creeper has an x (side-to-side) and y (up and down) position that can be changed once per second. How would you tell the computer to do this?

Every second, increase or decrease the x (side-to-side) position of the creeper by a set number.


Suppose N represents a very large number like 1 Billion. Sara claims that N is the largest number. Why is she wrong?

Suppose N is the largest number. Now, add 1 to N. This new number is larger than N, contradicting that N is the largest number. For example, if N is 1 million, we can add 1 and get 1 million and 1. This process of making an argument in math is called a proof, and it's what professional mathematicians do all the time to make claims about numbers that we use all the time!


An ice skater spins one with their arms stretched out wide and once with their arms tucked in. Which spin was faster and why?

The spin when they tucked their arms in was faster. This is because their angular momentum--what physicists use to measure how much weight weight is rotating and how fast--depends on their radius--how wide they are. A larger radius is harder to rotate. This is also why it's easier to rotate a small pencil than a long stick.
How does an earthquake happen?

An earthquake happens when two tectonic plates--slabs of earth move and strike each other. The earthquake is the result of the collision. The earth's surface rests on a layer of molten lava, and sometimes these pieces move!


suppose you had a list of numbers and wanted to find the lowest number. Also, you can only compare two numbers at once, and store one number at a time. How would you tell a computer to find the lowest number?

Store the first number and assume it's the lowest number. Compare it to the second number and store the lower one. Compare that new number and the third number and store the lower one. Keep doing this until the last number. The stored number is the lowest number.

a = 2, b = 5, c = 1.

What is (a - a) + (b - b) + (c - c)?

the answer is 0. In fact, you don't even need to do any work to solve this problem! When we subtract any number from itself we get 0 (1-1=0, 2-2=0, 3-3=0, ...), so a-a=0, b-b=0, c-c=0, and 0+0+0=0.


You have two identical balls. At the exact same instant, you drop one and throw one as far as you can horizontally, and both are released from the same height. Which hits the ground first?

Both balls hit the ground at the same time. the balls have different sideways motion but have the same downwards motion, which is just the action of gravity on the balls.


Can you freeze oxygen (air)?

Yes! Almost all elements have 3 states of matter: solid, liquid, and gas, like we see with H2O (water) in the form of ice, water, and gas. You'll probably never see frozen oxygen since it freezes at a temperature 12 times lower than water, but this is possible on the moon!


In a family, a child has two parents. Each of those two parents also have two parents. How many people are in this family tree?

There is 1 child, 2 parents, and 2 * 2 = 4 grandparents (two for each of two parents). This makes 1 + 2 + 4 = 7 people in the family tree. In computer science, trees are used to model things like families, where each person--or node in a tree--has two things connected to it, like two parents in our family tree.


Suppose there are 101 letters and 100 mailboxes. If the mailman tries to put each letter in a different mailbox, how many letters have to share a mailbox?

Two letters have to share a mailbox at minimum. The mailman can put the first 100 letters in unique mailboxes, but the 101st letter has to go in one of the mailboxes that already has a letter in it, so it is guaranteed that at least 2 letters share a mailbox. In mathematics, this is called the pigeonhole principle (imagine pigeons and holes instead of letters and mailboxes) and is used all the time!

Click to zoom