UNIT 02
DRIVEWAY PHYSICS
IT’S FUN TO MAKE THINGS FLY THROUGH THE AIR. Designing and assembling water rockets attached to produce-bag parachutes is a great way to explore aeronautical engineering. Backyards and driveways are perfect venues for testing other simple physics concepts as well, including centripetal forces, the Bernoulli effect, and even optics. And if you want to play with projectiles, you can make a catapult.
Catapults were first invented as tools of war. The earliest catapults, called ballistas, were like giant crossbows. Mangonel catapults have long wooden arms with buckets at the end, and the tension is stored in a rope. Trebuchet catapults were designed to inflict maximum damage using a heavy counterbalance to launch projectiles that destroyed castle and city walls. Warriors flung a multitude of deadly objects at and over fortress walls, including stones, flaming chemicals, and burning tar.
This unit shows you how to make a smaller, less destructive version of a mangonel catapult in your own driveway, using a chip-bag clip and some paint sticks.
LAB 05
PRODUCE-BAG PARACHUTES
DESIGN AND CONSTRUCT PRODUCE-BAG PARACHUTES TO SLOW THE DESCENT OF A WATER ROCKET YOU SHOOT SKY-HIGH USING A BIKE PUMP.
MATERIALS
Scissors
Empty 12 × 12-inch (30.5 × 30.5 cm) produce bag or other lightweight bag
Glue dots
String, yarn, or embroidery thread
Duct tape
Empty 34 fluid ounce (1 L) bottle
Ball inflation needle
Cork that fits snugly in the mouth of the bottle, cut in half widthwise to form two smaller corks
Bike pump
Water
Safety goggles
Shoe box or similar container
SAFTEY TIPS & HINTS
— Safety goggles should be worn when shooting off water rockets.
— An adult should cut the cork in half and put the inflation needle through it.
PROTOCOL
STEP 1: Cut a produce or other lightweight bag into a 12 × 12 inch (30.5 × 30.5 cm) square to use as a parachute.
STEP 2: Cut four pieces of string, yarn, or thread, each about 12 inches (30.5 cm) long. Use glue dots to firmly attach one string to each corner of the parachute.
STEP 3: Use duct tape to firmly attach the parachute strings to the bottom of a plastic bottle. (Fig. 1)
Fig. 1: Tape the parachute strings to the bottom of the bottle.
STEP 4: Push the ball inflation needle through the cork and attach the needle to the bike pump. (Fig. 2)
Fig. 2: Push a ball inflation needle through a cork and attach it to a bike pump.
STEP 5: Fill the bottle about a fourth of the way up with water and plug it tightly with the cork attached to the bike pump. (Fig. 3)
Fig. 3: Add water to the rocket.
STEP 6: Put your safety goggles on and set the plastic bottle rocket in a container, such as a shoe box, so the bottom of the bottle is pointing up and away from you.
STEP 7: Pump air into the rocket with the bike pump until you have lift off. (Fig. 4)
Fig. 4: Shoot your rocket into the air to test the parachute you made.
STEP 8: If your experiment didn’t work the way you hoped it would, reengineer your parachute and try again!
CREATIVE ENRICHMENT
1. Change the shape and design of your parachute. What happens if you add holes or more strings?
2. Add different amounts of water to your rocket to see how high it will fly.
LAB 06
CRAZY CATAPULT
CONSTRUCT A MINI CATAPULT FROM PAINT STICKS AND SPRING CLAMPS.
MATERIALS
3 or more wooden paint stirring sticks
Spring clamp, such as a chip-bag clip
Wire
Duct tape
Nails
Hammer
Sturdy piece of wood or wooden box
Paper cup, with the top two-thirds cut off
SAFTEY TIPS & HINTS
— Never use your catapult to shoot projectiles at a person.
PROTOCOL
STEP 1: Securely attach one paint stick to each handle of the spring clamp using wire and duct tape. The sticks essentially lengthen the spring clamp, forming a large V with the clamp at its point.
STEP 2: Place the third paint stick so that it lies lengthwise along one end of the V and nail the overlapped sticks to a wooden board or box, leaving the other end of the V sticking up into the air. (Fig. 1)
Fig. 1: Nail the two overlapped sticks to a wooden board or box.
STEP 3: Tape the paper cup to the top of the stick in the air to make a launcher for the catapult. (Fig. 2)
Fig. 2: Tape a paper cup to the upper arm of the catapult.
STEP 4: Place a small item, such as a dry bean or a marshmallow, in your catapult, pull the top stick all the way down, and then release it. (Fig. 3, 4)
Fig. 3: Add an object to the cup and pull the arm back.
STEP 5: Launch several items of different sizes and measure how far they travel. Can you predict where the items will land?
CREATIVE ENRICHMENT
Change the length of the arm of the catapult. Do you think a longer arm or a shorter arm will shoot objects farther?
LAB 07
CARDBOARD–BOX PROJECTOR
ENGINEER A VIDEO PROJECTOR FOR YOUR PHONE OR TABLET USING A BOX AND A MAGNIFYING LENS.
MATERIALS
Cell phone or electronic tablet
Shoe box (for cell phone) or large cardboard box (for tablet)
Magnifying lens or magnifying sheet
Cutting tool
Tape
Box or table, to set up projector
Flat white surface, for the screen
SAFTEY TIPS & HINTS
— This project requires some cutting with sharp tools and may be better for older kids.
— A homemade projector will not produce high-definition images because hand-held devices don’t emit enough light, but this is a fun way for kids to learn a little science and watch videos.
PROTOCOL
STEP 1: Turn the light setting and volume on your device all the way up.
STEP 2: Set your phone or tablet down against one end of the box, flush with the cardboard, and mark where the top of your device touches the box.
STEP 3: Line up the top of your magnifying lens or sheet with your mark on the box, trace it, and cut a hole slightly smaller than the size of your magnifier. Cut the opening so that when you place your device on the opposite side of the box, the center of your device will line up approximately with the center of your magnifier. You may have to remove the lens from the holder of a magnifying glass to center it. (Fig. 1)
Fig. 1: Cut an opening for the magnifier.
STEP 4: Tape the lens into the hole you cut. If you are using a magnifying sheet, be sure that the grooved side faces in and the smooth side faces out. (Fig. 2, 3)
Fig. 2: This is a page magnifier in a box projector.
STEP 5: Lock the portrait orientation on your phone, so the image can’t flip, and open a photo to focus on.
STEP 6: Test your projector when it’s dark outside or in a dark room. Turn the device upside down, placing it in the box on the side opposite the lens.
STEP 7: Set your projector on a box or table and focus your image on a flat white surface, such as a garage door, paper, or a sheet. You will have to play around with the distance between the projector and the screen, depending on the distance between the device and the lens and the magnification. To make the image larger, move the box away from the screen and move your device forward inside the box to get perfect focus. Remember to keep the device screen at a 90-degree angle with the bottom of the box. (Fig. 4)
Fig. 4: Adjust the distance and focus your image.
STEP 8: When you have the focus set, start your movie, secure the device to the back of the box, close the lid, or cover the box with a towel to block out excess light, and enjoy the show! (Fig. 5)
Fig. 5: Enjoy the show!
CREATIVE ENRICHMENT
1. Can you design a better projector? How does the size of the box affect the image?
2. What happens to the image if you add a second lens to your projector?
3. Can you make an even bigger, sharper image with a laptop that produces more light?
LAB 08
SOCK CENTRIFUGE
EXPERIMENT WITH CENTRIPETAL FORCES BY SWINGING A SOCK.
MATERIALS
Four 3- to 4-ounce (85 to 115 g) gelatin snack cups, preferably 2 different colors (e.g., red and green)
20 marbles
Duct tape
2 socks
Piece of kitchen twine or heavy string about 4 feet (120 cm) long
Mouth and neck of a 2-liter bottle, cut off with scissors, or a short plastic tube with about a 3/4-inch (2 cm) diameter
SAFTEY TIPS & HINTS
— Marbles are choking hazards, so young children must be supervised.
— If you don’t have twine, put the gelatin cups in a long sock and just swing the sock in circles. This option is better for very young kids.
— Do not eat the gelatin.
PROTOCOL
STEP 1: Remove the covers from the gelatin cups.
STEP 2: Choose 2 cups that are the same color and cover them with as many marbles as will fit in a single layer. Don’t push the marbles into the gelatin. (Fig. 1)
Fig. 1: Cover the gelatin cups with marbles.
STEP 3: Flip the two remaining cups of gelatin over on top of the cups covered with marbles so that the openings face each other. Tape the cups together with a thin piece of duct tape around the middle, so you can see the marbles. (Fig. 2)
Fig. 2: Tape the gelatin containers together.
STEP 4: Put the taped gelatin cups into the toes of the socks with the same color gelatin closest to the toe of each sock. Record what color gelatin is closest to the toe.
STEP 5: Put the string through the bottle neck or tube and securely tie one sock to each end of the string.
STEP 6: With one sock resting on the ground, grasp the bottle neck or tube with your right hand and hold the string under the bottle neck or tube tightly with your left hand.
STEP 7: Stand up and swing the bottle neck or tube in circles with your right hand above your head, so the sock above it swings in a circle. Use your left hand to control your centrifuge. The string in your left hand will pull up as you swing harder.
STEP 8: Swing the sock harder. Spin it around your head as many times as you can. Take a break if you need to, but try not to bang the gelatin cups against the ground. (Fig. 3, 4)
Fig. 3: Swing the gelatin sock in a circle over your head.
Fig. 4: If you don’t have string, make a centrifuge with a long sock.
STEP 9: Remove the gelatin from the socks, and observe the marbles. (Fig. 5)
Fig. 5: See what happened to the marbles you spun.
CREATIVE ENRICHMENT
1. Test what happens if you change the amount of weight in the bottom sock. How much weight do you have to add to swing the upper sock in a circle slowly without holding on with your left hand?
2. Make concentration gradients with colored gelatin and test how different-size marbles move through them using your sock centrifuge. Make sure you have the highest density gelatin on the bottom of the cup.
LAB 09
THE BERNOULLI EFFECT
INFLATE A NEWSPAPER BAG BALLOON WITH A SINGLE BREATH, AS IF BY MAGIC.
MATERIALS
Scissors
3 narrow plastic newspaper bags
Glue dots or double-sided tape
SAFTEY TIPS & HINTS
— Supervise small children around plastic bags.
PROTOCOL
STEP 1: Cut the ends off of two of the newspaper bags. (Fig. 1)
Fig. 1: Cut the ends off of two newspaper bags.
STEP 2: Glue or tape the three bags together to form a single long bag with the uncut bag forming a closed end. (Fig. 2)
Fig. 2: Glue or tape the ends of the bags together to form a single bag.
STEP 3: Put the bag to your lips and see how many breaths it takes to inflate it. (Fig. 3)
Fig. 3: Hold the bag up to your lips and try to blow it up.
STEP 4: Now, with someone holding the opposite end of the bag up off the ground, position the bag a few inches (8 to 10 cm) away from your lips and blow a long, steady stream of air into it. If you do it correctly, the bag should inflate with a single breath. (Fig. 4)
Fig. 4: Hold the bag a few inches (8 to 10 cm) from your lips and inflate it with a thin stream of air.
CREATIVE ENRICHMENT
Come up with more experiments to demonstrate Bernoulli’s principle.