Inside the Mechanical Clock

Description:

This is an activity that will help the student visualize how gears turn. In this activity they can discover the rotational pattern of gears meshed together. They will also see the relationship between the number of teeth to the number of turns. (Ratio's) As a follow-up activity, the teacher can then focus on how the hands of a clock move in relationship to the gears. (See the last discussion question)

Materials:

Print a copy of the gears(click to find the gear patterns)

card stock or tag board

8 X 11 corrugated cardboard (one for each pair of students)

small colored stickers (they should fit on one tooth of each gear)

thumbtacks or push pins (about 5 they are for the center of each gear)

scissors

glue sticks (If you don't use card stock or tag board)

Hypothesis:

When you turn the first gear in a gear train of 5 gears, how can you predict the direction the last gear will move?

Advanced Preparation:

Group the students in fours but have enough materials for them to work in pairs within the group.
If you are using card stock ore tag board make copies of the gears on the tag board. If a copy machine is not available then the students should glue them on to the card stock or tag board.
Remind the students to be careful as they cut the gears. The more time they take cutting the gears the better the turning of the gears.
You can get corrugated cardboard from a grocery store or ask students to bring it in. (Sometimes you can find people who have just moved and have cardboard boxes left over.) Foam board could be used also. Cut the cardboard to the 8 X 11 size. There should be one for each pair of students.
The teacher should try this activity before presenting it to the class.

Procedure:
1. Before you pass out the materials, discuss the hypothesis with the tire class. On the board write down their ideas. (You could also put the answers on bulletin board paper and keep track of each class.)
2. Pass out the materials to the groups. (Glue and scissors could already be on the tables.)
3. If the students need to glue the gear patterns onto the card stock or tag board have them do it now.
4. Next the students should cut out the gears. Remind them to be very careful and follow the lines.
5. Once the gears have been cut out the students take one sticker and place it on only one tooth of each gear. This will help mark where the gear begins to turn.
6. Next have the students count the number of teeth on each gear. They then put that number on the gear.
7. The students should now fold down each tooth on each gear. This will raise the gear up just enough to let it turn and let the other gears touch each other.
8. Now use a thumbtack or push pin to attach the gears to the 8 X 11 corrugated card board. The gears should touch and the teeth should mesh together. The students begin with just two gears touching and try to turn them. (They may have to help each gear turn.) Then they record their turns on a data table. Data Table: (Click for a print copy)
9. Next the students discuss their observations with the other students in their group. The group should then choose a spokes person to explain their findings to the class. The teacher should record the findings on the board or bulletin board paper.
Discussion Questions:
(The students share their observations before trying these questions.)
- With a gear train, how do you determine how many turns each gear will make to return both gears to their starting positions? (This is where the small sticker on the tooth will help students visualize the number of turns.)
- Which size gear turns the fastest? ( In other words to make the large gear turn one time how many turns does the smallest gear turn?)
- Is there a pattern in the teeth ratios and turn ratios.
- How do different sized gears change the speed of a bicycle?
- In a clock, all three hands (the second, the minute, and the hour hand) rotate in the same direction at different speeds, how might their gears be connected? (Have the students demonstrate this pattern with their gears.)
Variations:
- Lego™'s, K'NEX, and FischerTechniques™ all have ars. You could use these instead of the cardboard gears. They can be obtained in toy stores or even at garage sales.
- You can obtain lids from various size "to-go" drink containers. Then cut corrugated cardboard into strips the with of the lids. Glue the strips on to the lids and they will make gears.
Science Connections:
- Gears can be used to transfer forces from one part of a machine to another.
- A machine is a device for multiplying forces or changing the direction of forces.
- Mechanical energy is the energy due to the position or the movement of something.
Journey In Time || The Science of Gears || Lessons