# Motivating high school Physics students with Popcorn Physics

• BRUCE A RATCLIFFE
In summary, the conversation revolved around the topic of teaching physics and keeping students engaged and interested. The speaker shared their experience of using project-based learning and gave an example of a lesson involving popcorn. They also discussed a problem involving two people eating popcorn together and shared different approaches to solving it.
BRUCE A RATCLIFFE
How did you find PF?: Quiet Desparation prompted me to search for "Electronic forums"

I've been teaching physics for forty five years (quadruple alliteration : ) Though I would dearly love to teach a rigorous, math-based course, if I did so, my clientele would be lost, bored and gone. My students taking Calculus are oft times stopped cold by 1/2 X 1/3 = ?

My solution? ACTION! Projects where students are cooperating, building, testing, deploying and analyzing some project seems just the thing to keep students eager to come to class. (see Egg Drop preparation: ). These sorts of "lessons" last a lifetime:

Popcorn Physics? It was an accident that we spent two months on. Turns out a whole lot of physics was involved, but it started out with a microwave popcorn thief:

[Personal information removed]
45 years into it, and hoping for 20 more!

Last edited by a moderator:
The problem I like to give non-physics students involving popcorn is: If Bob can eat a bag of popcorn in twenty minutes, and Mary can eat a bag in thirty minutes, how long does it take Bob and Mary to eat one bag when they both eat it together?

Many do not get this one correct, but most understand the solution when I tell it to them.

When they get stuck, sometimes I will give them the hint of how many bags can they eat in an hour?

Last edited:
MatinSAR, vanhees71 and berkeman
The problem I like to give non-physics students involving popcorn is: If Bob can eat a bag of popcorn in twenty minutes, and Mary can eat a bag in thirty minutes, how long does it take Bob and Mary to eat one bag when they both eat it together?
That's a trick question. Just sayin'.

I'm not sure if this is what you call an elegant solution. Maybe cumbersome would be a better descriptor. But here's my solution: It is a rate problem.
Bob: 1 bag/20 min
Mary: 1 bag/30 minutes.
To add fractions you need a common denominator:
Bob: 1bag/20 min = 3 bag/60 min
Mary: 1 bag/30 min = 2 bag/60 minutes
Team B&M together will finish off 5 bag/60 minutes.
Which is (5/5 bags) / (60/5 minutes)
So 1 bag will be gone in 60/5 minutes = 12 minutes
QED

It is much easier solved with what is probably not the best mathematical technique in that it switches back and forth with units, but still fairly easy to follow:

Bob can eat 3 bags in an hour, and Mary two, making for 5 bags in an hour, or twelve minutes per bag.

Sticking with minutes only and working the rates is more systematic, but the arithmetic becomes more difficult then, so the lay person usually prefers the simpler albeit unsystematic approach.

Edit: Computing it more systematically by computing rates per minute, adding the rates, and then setting ## rate_{total} \times time= 1 ## and computing the time makes for a more difficult arithmetic exercise.

Last edited:
PhDeezNutz and vanhees71
TOO funny, Charles! I was proud of my solution, featuring units analysis AND fractions--the terror of my students. And then I see your oh-so-simple solution.
Bruce

I sometimes like the random approach. By the time Mary has eaten one bag, Bob has eaten 1.5 bags. That's 2.5 bags in 30 minutes, or 12 minutes a bag.

PeroK said:
I sometimes like the random approach. By the time Mary has eaten one bag, Bob has eaten 1.5 bags. That's 2.5 bags in 30 minutes, or 12 minutes a bag.
Similar to my immediate approach, but I used Bob. After 20 minutes, Bob has eaten one bag and Mary 2/3 of a bag. That’s 5/3 bags in 20 minutes, so 3/5 of that time for one bag, so 12 minutes.

The exercise work rates problem in post #2 is or seems like a typical routine exercise being so many like that one. But I did not look into that particular one very carefully; just it seems so familiar in type.

My solution, still a typical way to solve:

my solution: combined constant rates, eating bag of popcorn
Maybe slightly differently arranged but like this:
rate=quantity/time

from it find that (rate)(time)=quantity

Bob's rate, 1/20 the unit in bag per minutes

Mary's rate, 1/30

Bob and Mary Combined, 1/20+1/30

and to simplify

30/(30*20)+20/(20*30)

(30+20)/600

50/600 and this is bags per minutes;

5/60

But you want how much time for 1 bag,
then the reciprocal of the rate

60/5

12 MINUTES per BAG

Last edited:
See https://www.physicsforums.com/threa...ns-around-a-central-coin.971465/#post-6176083 for another fairly simple problem that I try to motivate students with. It's a good application of the law of cosines. See also post 4 where the 8 pennies are close to a perfect fit around the JFK 50 cent piece.

Last edited:
Since Bob eats 1.5 times as fast, he'll eat 60% of it, while Mary finishes the remaining 40%. Since Bob eats 1 bag in 20 min, he'll eat 60% of the bag in 12 minutes.
Then I'll ruin it by saying neither eats at a uniform rate.

## 1. How does popcorn physics relate to high school physics?

Popcorn physics is a fun and engaging way to introduce high school students to basic concepts of physics. By using the properties of popcorn, such as its expansion when heated and the force of gravity, students can explore and understand key principles of physics in a hands-on and memorable way.

## 2. Can popcorn physics be used for all levels of high school physics?

Yes, popcorn physics can be used for all levels of high school physics. It can be adapted for introductory courses as well as more advanced courses, depending on the specific concepts and experiments chosen.

## 3. What are some examples of experiments that can be done with popcorn physics?

Some examples of experiments that can be done with popcorn physics include measuring the expansion of popcorn kernels when heated, studying the effects of different temperatures and cooking times on popcorn, and exploring the force of gravity by dropping popcorn kernels from different heights.

## 4. How can popcorn physics be used to motivate students?

Popcorn physics can be used to motivate students by making the subject more fun and relatable. By using a familiar and enjoyable snack, students may be more engaged and interested in learning about physics. Additionally, the hands-on nature of popcorn physics experiments can help students see the real-world applications of the concepts they are learning.

## 5. What are the potential benefits of using popcorn physics in the classroom?

Using popcorn physics in the classroom can have several benefits. It can make the subject more enjoyable and engaging for students, leading to increased motivation and understanding. It can also help students develop critical thinking and problem-solving skills as they design and conduct their own experiments. Additionally, using a hands-on approach can help students retain information better and apply it to real-life situations.

• STEM Educators and Teaching
Replies
8
Views
2K
• STEM Educators and Teaching
Replies
7
Views
4K
• New Member Introductions
Replies
4
Views
126
• STEM Educators and Teaching
Replies
15
Views
4K
• STEM Educators and Teaching
Replies
6
Views
3K
• STEM Educators and Teaching
Replies
11
Views
3K
Replies
4
Views
816
• STEM Career Guidance
Replies
26
Views
1K