Gravity NGSS MS-PS2-4

In the Gravity mini unit, students demonstrate acceleration due to gravity by dropping objects (basketballs, golf balls etc.) and showing they fall at the same rate, regardless of mass. Then, students analyze data including planetary mass, surface gravity and orbital period. Finally, students calculate the weight of a basketball on different planets and figure out what it would be like to play their favorite sport on Jupiter or the sun!

Extension activities challenge students to learn about how tide pool animals (sea stars, sea urchins, anemones, Pacific octopus) have adapted to live in these shallow, salty waters!

Anchor Phenomenon Ideas: Share the Mass and Surface Gravity data table with students and record the questions they generate. Or, simply drop two balls of different sizes (a marble and a basketball) off the edge of the table. Use the questions your students come up with to make connections throughout your unit.

Make it Relevant: We start the unit with this TED-Ed animation - How to think about gravity to help kids make connections with this challenging topic.

Tips and Tricks: Students find it confusing when we say that mass does not affect gravitational pull (we show them objects of different masses fall at the same rate) but then we compare the mass of planets with their surface gravity and conclude mass DOES affect gravity.

It is important to clarify this contradiction. An object's mass does affect its gravitational pull but only when we are talking about HUGE masses.

Practice analyzing data tables together as a whole class mini-lesson. Remind students to read all of the labels, write notes and questions directly on the tables and to look for patterns. They can also rewrite data in a different way if that will help with understanding.

Savvy students will point out that Uranus has significantly greater mass than Earth but slightly less surface gravity - Saturn also has greater mass but less surface gravity than Neptune. These anomalies can be explained by the differing densities of each planet.

Also, middle school kids DO NOT want to calculate their weight on different planets. We calculate the weight of a basketball instead.

Enrichment Ideas: Susan Beth Pfeffer's young adult series, Life as We Knew It, tells the dystopian story of life after an asteroid hits the moon and moves it much closer to Earth. Middle schoolers love these four books and we cannot keep them on our classroom shelves! This is an excellent way to connect real science with science fiction. Could this really happen?

Share excerpts with the whole class or offer copies of the books for kids to read as they finish the mini unit. See our Multiple Intelligences Book Project for more ideas!