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Open-and-go lessons that inspire kids to love science.

Science curriculum for K—5th grades.

90 sec
  • Hands-on lead students in the doing of science and engineering.
  • Standards-aligned science lessons Cover core standards in 1-2 hours of science per week.
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Invisible Forces

Forces, Motion, & Magnets

3rd Grade, 4th Grade, 5th Grade

NGSS Standards covered: 3-PS2-3 , 3-5-ETS1-1 , 3-PS2-4 , 3-5-ETS1-2 , 3-PS2-2 , 3-5-ETS1-3 , 3-PS2-1
In this unit, students explore the forces all around them. They investigate the effects of balanced and unbalanced forces, the pushes and pulls of bridge structures, and the effects of friction on the motion of objects. Students also explore the power of magnetic forces and investigate firsthand how these forces can be used to help us in our everyday lives. Less
  1. Lessons
  2. Activity Prep
  3. Assessments

Lesson 1: Balanced & Unbalanced Forces

Hopper Popper

In this lesson, students will see that by learning to think about pushes and pulls — forces — they can accomplish extraordinary things! In the activity, Hopper Popper, students make a folded piece of cardboard jump high in the air, propelled by the pulling force of a rubber band. They discuss the forces involved in making this “Hopper Popper” jump.

Number of students:
High Hop Scorecard worksheet 30 copies
Hopper Popper Teacher Tips worksheet 1 copy
Launch Pad printout Print 30 copies
30 pens
30 rulers
30 pairs
Recycled cereal boxes also work.
4 square feet
Rubber Bands (#16)
60 bands
Prep Instructions

In this activity, each student will make their own Hopper Popper, but we suggest they work in pairs when they launch their poppers. Homeschool students can work on their own, but may need a partner to help when it comes time to launch their Hopper Popper. Some teachers choose to have students wear safety glasses for this activity since Hopper poppers can hop high!

Prepare the Chipboard

If you want your students to practice measuring, you can have them cut 3” x 6” rectangles from chipboard before you begin this lesson. If you don’t have time for students to measure and cut rectangles, we recommend you cut the chipboard into 3” x 6” rectangles before class. It doesn’t take long if you use a paper cutter.

Supplies for Open-Ended Exploration (Optional)

At the end of the activity, we suggest that students change one variable to see how this affects their Hopper Popper. For this open-ended exploration, you can supply students with extra chipboard, extra rubber bands of different sizes, or extra rubber bands of different thicknesses. The Teacher Tips printout will help you guide students during this open-ended exploration.

Lesson 2: Balanced Forces & Engineering

Paper Bridge Engineering

In this lesson, students will learn about real-life bridge design. In the activity, Paper Bridge Engineering, students will use their knowledge of forces to build a strong bridge that supports as many pennies as possible -- using only paper.

Number of students:
Bridge Challenge worksheet 15 copies
Bridge Designer’s Notebook worksheet 30 copies
Building Bridges Teacher Tips worksheet 1 copy
Blank Paper (8.5 x 11")
90 sheets
Hardcover Books
90 books
30 rulers
30 pairs
We recommend having at least 400 pennies on hand for a classroom. Some bridges are VERY strong.
400 coins
Prep Instructions

We suggest students work in pairs. Homeschool students can work on their own.

Prepare With Some Engineering Inspiration

We recommend you watch this video of Doug & Pat from the Mystery Science team modeling how to build and improve a bridge. If your students get stuck, you can use this video for inspiration. Our Teacher Tips printout also provides suggestions for guiding students when they are building bridges.

Lesson 3: Friction & Pattern of Motion

The Great Slide Challenge

In this lesson, students will learn about friction (the force that slows you down on a playground slide). In the activity, The Great Slide Challenge, students work in groups of four to test which materials have the most friction and which materials have the least friction. Each group makes a model of a slide using a stack of books and a piece of cardboard, and makes "sliders" out of different materials.

Number of students:
Friction Investigation worksheet 30 copies
Hardcover Books
Used to prop up one end of the slide.
24 books
8 rulers
You can also use recycled cardboard cut into 1-inch squares.
16 square inches
Craft Foam
Can also use thin styrofoam.
16 square inches
Glue Dots
Tape will also work. We prefer sticky glue dots because they are easier to distribute in a classroom.
160 dots
Large Plastic Buttons
You can also use recycled plastic bottle caps.
16 buttons
16 square inches
Stiff Cardboard
Needs to measure at least 12" by 16." Recycled is fine. The lid of a cardboard file storage box works well.
8 pieces
Used as weights on the "sliders."
96 coins
Prep Instructions

We suggest students work in groups of four. Homeschool students can work on their own.

Prepare Testing Materials

Each of the materials that students will be testing as “sliders” needs to be about the same size. So before class, cut the chipboard (or cardboard), craft foam (or styrofoam), and sandpaper into 1-inch squares.

Make Model Slides

Each group first needs to make a model of a slide using books and a piece of cardboard. It should look something like this:

Slide Challenge Model

Separate Materials for Classroom Distribution

We suggest providing each group with 1-inch squares of each material that you have prepared prior to class, plus plastic buttons (or plastic bottle caps) and metal bottle caps (or large metal coins). Each group of four will also need about 20 sticky glue dots. You may want to separate or group these materials for easier classroom distribution. Groups will need two of each slider material so that they can do a fair test with different numbers of pennies.

Slide Challenge Supplies

Lesson 4: Magnets & Forces

Magnet Discovery

In this lesson, students will explore the surprising properties of magnets and experiment with an invisible force that acts at a distance. In the activity, Magnet Discovery, students use ring magnets and common objects to discover the push and pull of magnets and how magnets attract certain types of metals.

Number of students:
Ideas for Magnet Experiments worksheet 30 copies
Magnets Are Weird worksheet 30 copies
Magnetic Metal Items
Paper clips, staples, nails, washers, binder clips, metal bottle caps, stainless steel flatware, or anything else made of iron or steel.
30 items
Non-Magnetic Metal Items
Pennies, quarters, dimes, nickels, the metal band on the end of a pencil, aluminum cans, or anything else made of aluminum, copper, silver, or gold.
30 items
Non-Metal Items
Anything made of plastic, wood, glass, or paper. You can even try food items!
30 items
30 pencils
Index Cards (3x5)
60 cards
Paper Clips
120 clips
You can also use string or light ribbon.
15 feet
Ring Magnets
60 magnets
Prep Instructions

Set Up Magnet Test Items

The test items should include some metals that are attracted to magnets, some metals that are not, and some non-metal items. At a minimum, students should examine one item from each of these categories. You may want to set up a test item station so that students can explore multiple items from each category.

Cut Up String

Before class, cut up the string so that each student can have some for their experiments.

Teacher Tip

Magnets are fragile, so be careful. If you smack them against each other too hard, they will break. We trust you’ll be gentle with them, but just in case, it can’t hurt to wear safety goggles.

Lesson 5: Magnets & Engineering

Invent a Magnetic Lock

In this lesson, students investigate magnetic attraction and repulsion. In the activity, Invent a Magnetic Lock, students apply their scientific ideas about magnets to create a useful product: a magnetic lock that can open a paper door. Students engage in the engineering design process to test and improve their designs.

Number of students:
30 pairs
30 sheets
Dot Stickers
Pieces of tape will also work. We prefer dot stickers because they are easier to distribute in a classroom.
180 stickers
Index Cards (3x5)
60 cards
Paper Clips
30 clips
Paper Fasteners
30 fasteners
Post-Its (3")
30 post-its
Ring Magnets
30 magnets
Prep Instructions

Sort Materials Into Two Piles

Each student will first make a paper door using cardstock, scissors, and a post-it note. Then, students will design a lock for their door using a magnet, paperclip, paper fastener, stickers, and index cards. You may want to sort your materials into two piles for easier distribution.

Be Prepared for Some Troubleshooting

In this activity, students are asked to create something new -- an essential part of the engineering process, but one that may confuse or frustrate them. Below are some of the more common difficulties we found during our own testing, and the solutions we came up with.

  • Brads won’t puncture paper: Students may have trouble puncturing the paper with the brad. If this happens, use a sharp pencil to poke a small hole in the paper, then insert the brad.

  • Items won’t turn on the brad: The hole probably isn’t big enough. Twist the brad in a full circle a few times to enlarge the hole.


  • The magnet doesn’t make the lock move: Every lock will work differently, but it’s typically friction that causes this problem. If a piece of your lock is supposed to move, be sure it can move easily. If it’s attached too tightly, your magnet may not be able to move it.

  • Pieces keep getting stuck against one another:

    • If your lock keeps getting stuck, try rounding the edges of the moving parts. lock troubleshoot #1 lock troubleshoot #2
    • If the lock is getting stuck because a piece of paper is bending the wrong way, you can make the paper stiffer by folding it and adding stickers or paper clips to hold it together.

lock troubleshoot #3

  • Walls keep falling down: If you need help getting your wall to stay up, clip the 1-inch fold on the back to a clipboard, or slide it under the edge of a heavy book.

lock troubleshoot #4