Pet Puzzle

Instructions

I N PA R T N E R S H I P W I T H

A LESSON IN PHYSICS

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GETTING STARTED

Before we get started with our physics experiments and animal behavior exploration, let’s build

the puzzle!

When you receive your kit, you will find a single piece of jute twine, a plastic cup with three sets of

holes on the sides, and two pushpins. Using these items, we will create a suspended cup that you

will fill with several treats. Your pup can then approach and explore the puzzle and figure out how

to dump the treats for an encouraging surprise!

STEP 1

Thread the jute twine through the lowest holes in the cup.

STEP 2

Take each loose end of the jute twine and tie a knot to the pushpins by following the picture

below.

Note: In the next step we will be installing the puzzle using the pushpins. Please

ask an adult if it’s okay to use the pushpins on your walls! If you do not want

to use the pushpins, you can tie the jute twine to two chairs, under a table, or

any other creative way you can think of!

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STEP 3

Find a stable structure to set up your pet puzzle! Fasten your puzzle to your stable structure like

the images below. The puzzle should be approximately 2 ft. off the ground (think doggo height!).

Make sure both ends of the jute twine are at the same height. Once your cup and jute twine are

pinned or tied to the doorway, chairs, or table you are ready to test!

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EXPERIMENT 1

Lesson: Center of Gravity

What is "center of gravity"?

If you throw a ball straight up in the air, gravity will pull it straight back down. Not everything in

the world is as simple as a ball, however. This means that gravity will act on more complex objects

in more complex ways. One simple rule though is that all objects have a center of gravity. A

simple object such as the ball you through in the air ball has its center of gravity right at its

center. More complex objects depend on how the weight is distributed to determine their center

of gravity.

How does gravity work on more complex objects?

Your personal center of gravity is located roughly near your stomach at an infinitely tiny point. If

your center of gravity is roughly over the midpoint of your feet, your body will be balanced, and

you won't tip over. If you start leaning, everything changes. Stand up straight, then try leaning

forward without bending your legs. If you keep leaning, you will reach a point where your whole

body feels like it's about to topple over. Your head is one of the heaviest parts of your body. If

you lean forward, your center of gravity is no longer directly above the midpoint of your feet. The

more you lean, the more torque (pronounced “tork”) or turning force is created and the more

likely you are to topple over. Gravity makes your whole body rotate around your ankles as the

center point. Since you’re not as simple as the ball you throw in the air, gravity acts on you in a

more complex way.

To get a better understanding, compare the rotation point of your ankles to the hinge of the

door. When a force pushes an object that pivots (like a door on its hinges or you and your

ankles), the object will turn instead of moving in the direction in the force. Try opening a door by

pushing with one finger near the handle. Next, try opening the same door by pushing with one

finger near the hinge. Which one was more difficult? Pushing the door near the handle should

have been easier. For this same reason, taller objects are easier to tip over than shorter objects

because of the location of their center of gravity.

Let’s take these concepts and use them to explore how changing the center of gravity of our pet

puzzle can make it easier or more difficult for your pup to get a treat!

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Experiment Instructions

In this experiment, we will explore the impact of center of gravity on the design of our pet puzzle.

Using the holes at different heights on the sides of the cup, we will change the difficulty of

toppling the cup to get the treats!

STEP 1

Set up your pet puzzle with the jute twine threaded through the bottom set of holes. From our

quick lesson on center of gravity you may have guessed that the lowest set of holes is the easiest

to topple over. This will directly relate to your pup’s confidence level with the puzzle. See if you

can spot any body language cues you learned about in the HAWS presentation.

STEP 2

After your pup has had some time to explore the puzzle, move the twine up to the second or

third set of holes to increase the difficulty level. Your dog’s strength may also come into play here

as a smaller dog may not find it as easy to topple the cup when the jute twine is on the highest

set of holes.

STEP 3

Record your observations. Which set of holes worked best? Did your dog need encouragement?

Were any sets of holes too difficult or too easy? A good enrichment puzzle for a dog needs to be

the right level of difficulty.

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EXPERIMENT 2

Lesson: Centrifugal and Centripetal Forces

What are centrifugal and centripetal forces?

Centripetal force is defined as "the force that is necessary to keep an object moving in a curved

path and that is directed inward toward the center of rotation". Centrifugal force is defined as

"the apparent force that is felt by an object moving in a curved path that acts outwardly away

from the center of rotation".

The two are often confused because they are so closely related. The difference between

centripetal and centrifugal force has to do with different frames of reference or different ways

they’re viewed and experienced.

If you observe a rotating system (a car in a turn) from the outside, you see an inward centripetal

force acting to keep the car on the rotating path. However, if you are part of the rotating system

(you are in the car), you experience an apparent centrifugal force pushing you away from the

center.

It’s important to note that centripetal force is the actual force causing the object to stay on the

rotating path, whereas centrifugal force merely felt or observed by the system.

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Experiment Instructions

Using what we have learned about centripetal and centrifugal forces we will observe what

strategies best work for your pup to get those treats from the cup!

In our first experiment we changed the height of the twine to change the center of gravity of the

cup and in doing so, changed the difficulty of the pet puzzle. You may have noticed that as your

pet gained confidence with the puzzle, they tried to spin the cup faster. Depending on your pup’s

temperament, they may end up not flipping the cup over, or perhaps they spin it so fast no treats

fall out at all. Your pup might be confused, but since you now understand the centripetal forces

keeping those treats in the cup you can help you pup overcome this puzzle!

STEP 1

Set up your puzzle using the holes that worked best from Experiment 1.

STEP 2

Place the dog treats into the cup and use your hand to spin the cup as fast as you can on the

twine. If you do this quickly enough you will see that the treats do not fall out! If you can’t spin

the cup fast enough for this to happen, your pup will just get some extra treats

STEP 3

Take the cup off the doorway or chairs and thread the twine through the top set of holes.

STEP 4

Clear and area around you so you have plenty of space in all directions (no people, pets, or

obstacles in the way).

STEP 5

Take both ends of the twine in one hand and place a few dog treats into the cup. Gather the

loose twine in your hand so the cup cannot touch the floor while you hold it by the twine.

STEP 6

Swing the cup around in a circle like you’re continuously winding up to pitch a baseball. Again,

you should see if you swing the cup fast enough no treats fall out!

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STEP 7

Continue to experiment and record your observations. Try changing how much twine is between

your hand and the cup (making the swing circle larger or smaller). Notice now how you must spin

the cup faster when the twine is shorter. This is due to the velocity or speed of the cup. The

longer the string the faster the velocity and the less centripetal force (seen as tension on the

string) needed to keep the treats in the cup!

Don’t forget to give your pup some belly rubs for waiting while you tested centripetal forces!

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EXPERIMENT 3

Lesson: Degrees of Freedom

What are degrees of freedom?

Degrees of freedom tell us how many independent movements an object has. This lesson is best

learned through a hands-on experience. Let’s get to the experiment!

Experiment Instructions

STEP 1

For our first trial, we will explore how the angle of the twine affects the system. We are looking to

make the angle of twine as large as possible. To do this, adjust the ties on your pushpins or stable

structure like the images below.

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You will now notice that the cup can swing back and forth in addition to being able to rotate

around the twine in the middle. Why is this? What changed in our system? We added to the

degrees of freedom of the cup. When we increased the angle of the twine, we removed the

forward/backward swing constraint on the cup. It now moves more freely. Can you think of more

ways to add degrees of freedom to this system?

STEP 2

Test this setup with your pup! If your pup mastered the setup from Experiment 1, this version will

be an added challenge. Record your observations and remember to look for body language cues.

STEP 3

Continue to experiment with this setup by varying the angle of twine and recording your

observations. What angle is best for your pup?

STEP 4

Now we will combine the added degree of freedom from the twine angle with the center of

gravity concept we learned in Experiment 1. When varying the center of gravity by changing the

holes along with the angle of the twine you will find that you have added even more variability to

the puzzle. Continue to experiment until you find a setup that is personalized for your dog’s

enrichment needs. This may take some trial and error to get right so you will have to be patient

and help your dog learn what is best while you optimize your design.

Did you have fun learning about physics and playing with your pup? Do you want to make your

own more robust, optimized pet puzzle for your dog? Visit our Facebook page at

https://www.facebook.com/altrukits/ for instructions on how to make this design with simple

supplies from your local hardware store!

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REFERENCE LINKS

https://www.explainthatstuff.com/center-of-gravity.html

https://www.livescience.com/52488-centrifugal-centripetal-forces.html

https://www.smlease.com/entries/mechanism/what-is-degree-of-freedom-dof-in-mechanics/