Gravity at work Investigating Gravity s job in the solar system
Developed by: Betsy Mills, UCLA NSF GK-12 Fellow Title of Lesson: Gravity at Work! Grade Level: 8 th Subject(s): Gravity Summary: In this lesson, students will take their own experience of the effects of gravity, and use this to construct and understanding of how gravity works to shape larger objects in our solar system. Students will observe the role of gravity in toppling towers made of marshmallows, investigate the relationship between how round asteroids are and their mass, infer the role that gravity plys in this relationship, and finally predict which planet would have the tallest mountain (and on which planet one could build the tallest tower out of marshmallows!) Time Required: 90 minutes Group Size: Class should be divided into groups of 3-4 to complete this activity Cost to implement: ~$12 to $15 for marshmallows Materials List: Printed copies of asteroid pictures for each group 6 to 10 marshmallows per group (or per student) Rulers Calculators Safety Issues: Make sure students do not eat the marshmallows Learning Goals: Students will see the role of gravity in determining: why asteroids are different shapes why planets and stars are round the height of the tallest mountains Level of Inquiry: This lesson incorporates a low to medium level of inquiry. Students are provided a question and told what data to collect. Students then formulate their own explanation from summarizing the data they collect, and are guided to make a connection between this data and their understanding of gravity.
Background knowledge: Students should already have some familiarity with gravity, and its dependence upon the mass of an object (for example, the earth has more gravity than the moon). Introduction / Motivation: To open the lesson, have students divide into groups, and work with marshmallows to build the tallest tower that they can. Towers must be freestanding, and students should not be allowed additional materials (such as toothpicks) to aid in contruction. (Students should find that towers taller than 5 marshmallows are virtually impossible to build) Give students ~5 minutes to build their towers, and after building, have students come back together as a class and share the difficulties they encountered, and how high they were able to build their tower. Procedure: Ask students what was keeping their towers from being higher: why did they all fall down after reaching 4 or 5 marshmallows in height? Try to steer the discussion away from engineering, and toward gravity as the reason that ultimately, all the towers collapsed. Share the goals of today s lesson with the students: Think like scientists to understand how gravity does more than just make things on earth fall down. Ask students what they know about asteroids. Ask students, how you determine how round an asteroid is? (Experience shows that this is difficult for stuents to comprehend, they want to do things like go to the asteroid, take pictures of it from all sides, or put a string around it to see how curvy it is.) If students are stumped, try making an analogy to pictures of a rectangle drawn on the board. How would you say how much more rectangular one is than another? Try to get students toward the idea of comparing how long an asteroid is in one direction, compared to the other, maybe dividing the two lengths to get a roundness number or percentage of roundness. Return students to their groups, and give them pictures of asteroids to examine. Students will record the roundness and the mass of each asteroid in their data table. If students have a good background in math, have them graph their results (roundness vs. mass). Otherwise, have students make a second data table in which they order the asteroids by their mass.
After students have collected their data, bring the class together again to discuss. Did they notice any trends? What did the roundest asteroids have in common? What shape were the least heavy asteroids? Ask students, what could cause a relationship like this? What is different (besides roundness) for a less massive asteroid, compared to a more massive asteroid? (Students might think of weight, size, and hopefully gravity!) If students have difficulty understanding the connection, talk about it as a force balance. As an object gets bigger, the force of gravity gets stronger and stronger, until eventually, rocks aren t tough enough to stand up to that force. Gravity wins! It is like if you went to Jupiter-- you would just be flattened by its gravity, even if you tried to resist, you wouldn t have enough force to counteract the force of its gravity. Lesson Closure: To end the lesson, have students predict which planet would have the tallest mountain: Earth, Mars, or Venus, given only the mass of each of these planets. Students should be able to predict the order by height of each planet s tallest mountain (for example, Mt. Everest) and justify their answers. To bring the lesson full circle, ask where in the solar system students would want to go to build the tallest marshmallow tower. References: None List CA Science Standards addressed: 2g: Students know the the role of gravity in forming and maintaining the shapes of planets, stars, and the solar system. 4e: Students know the appearance, genral composition, relative position and size, and motion of the objects in the solar system, including planets, planetary satellites, comets, and asteroids. Attachments: Handouts of asteroid images to measure roundness Powerpoint slides for accompanyng lesson presentation
PROMETHEUS MASS: 2 x 10 17 KG AVERAGE SIZE: 50 KM
HYPERION MASS: 6 x 10 18 KG AVERAGE SIZE: 135 KM
VESTA MASS: 3 x 10 20 KG AVERAGE SIZE: 500 KM
EROS MASS: 7 x 10 15 KG AVERAGE SIZE: 15 KM
CERES MASS: 9 x 10 20 KG AVERAGE SIZE: 470 KM
IDA MASS: 4 x 10 16 KG AVERAGE SIZE:
PALLAS MASS: 2 x 1020 KG AVERAGE SIZE:
YOUR MISSION: WITH YOUR LAB GROUP, BUILD THE TALLEST TOWER YOU CAN OUT OF MARSHMALLOWS
WHAT STRATEGIES WORKED WELL? WHAT WERE THE MAIN PROBLEMS?
TODAY S GOALS: 1. UNDERSTAND WHAT GRAVITY DOES OTHER THAN JUST MAKING STUFF FALL DOWN 2. PRACTICE BEING A SCIENTIST!
SCIENTIFIC METHOD: HOW DO STARS FORM? (QUESTION) I THINK STARS FORM FROM DENSE CLOUDS OF GAS AND DUST (HYPOTHESIS) I WILL LOOK IN GAS CLOUDS FOR VERY YOUNG STARS (TEST HYPOTHESIS) ARE THE STARS FOUND NEAR GAS CLOUDS YOUNG OR OLD? (ANALYZE RESULTS) I WILL GO TO HAWAII AND TELL OTHER ASTRONOMERS ABOUT THIS! (REPORT FINDINGS)
YOUR JOB: MEASURE THE SIZES OF THE ASTEROIDS COMPARE THEIR MASS AND THEIR ROUNDNESS
ROUNDESS MASS #1 #2 #3
1 ROUNDESS 0 10 15 10 21 MASS
DESCRIBE WHAT YOUR GRAPH SHOWS. WHY DOES ROUNDNESS DEPEND ON MASS?
PREDICT: WHICH PLANET HAS THE HIGHEST MOUNTAIN? MARS (MASS = 6 x 10 23 kg) EARTH (MASS = 6 x 10 24 kg) VENUS (MASS = 5 x 10 24 kg)
DOES THE DATA SUPPORT YOUR HYPOTHESIS? MARS: OLYMPUS MONS, 27 km EARTH: MT. EVEREST, 9 km VENUS: MAXWELL MONTES, 11km
BASED ON YOUR EXPERIENCES TODAY, WRITE A SHORT PARAGRAPH ON HOW GRAVITY SHAPES OBJECTS IN THE SOLAR SYSTEM.