Gymnast

• Review the online pupil material. Use a projector to share this material with your pupils during the lesson.
• Consider pre-building the Gymnast model to use during the lesson to help pupils who are having trouble building.
• Make sure that you have covered the relevant concepts (i.e. Newton’s three laws of motion) in an earlier lesson.
• Consider the abilities and backgrounds of all your pupils. Differentiate the lesson to make it accessible to everyone. See the Differentiation section below for suggestions.

• Watch the pupil video here or access it via the online pupil material.

• Facilitate a quick discussion about the force that helps a gymnast swing on a horizontal bar.
• Ask questions like these:
  • Which force is required to make the gymnast move? (Gymnasts use push and pull forces with their muscles to generate forward momentum to overcome the force of gravity that is pulling them down).
  • What keeps the gymnast moving? (Newton’s first law states that an object in motion will stay in motion until it is acted upon by an external force. When their muscles stop pushing, the air resistance and friction between the gymnast’s hands and the bar will eventually bring them to a stop at the bottom of the bar because gravity pulls them down).
• Tell the pupils that they’re going to build a gymnast-powered car.
• Distribute a set to each group.

• Have the pupils work in pairs to build the Gymnast model. Tell them to take turns, one partner searching for the bricks while the other builds, switching roles after each step has been done.
• This model should only take 15 - 20 minutes to build. Once they have finished building, have the pupils find an open space and give it a go.
• You can find building help in the Tips section below.
• Next, ask them to perform the three experiments that are found in the pupil material for this lesson.

Experiment 1:

• Have the pupils use a strip of masking tape to mark a line and then swing the gymnast with the ratchet levers folded in and observe what happens.

Experiment 2:

• Next, have the pupils explore how they can make the pendulum car move forwards using the ratchet levers.
• Ask them to flip down the front ratchet lever on their cars.
• Have them place their models on the start line, pull the pendulum back 90 degrees and release it.
• Tell them to use a LEGO^® brick to mark the distance that their car travelled and to measure and record the distance on their worksheet (Teacher Support – Additional Resources).
• Now have the pupils predict how far their car will travel if they pull the pendulum back as far as it can go (i.e. around 160 degrees). Tell them to place another brick to mark the predicted distance (p).
• Have them test to see if their prediction was correct, and then record the actual distance travelled (a) on their worksheet (Teacher Support – Additional Resources).

Experiment 3:

• Have the pupils fold-in both ratchet levers. Explain that now they will observe what happens when they release the gymnast with the car resting against their hand.

• Gather your pupils together to share what they have observed in their groups.  
• Ask questions like these:
  • Why did the car move back and forth with both ratchet levers folded in? (It oscillates backwards and forwards because the net force is zero.)
  • Which forces are at work? (The force of gravity pulls the gymnast down. The momentum of the swing is rigidly attached to the pivot at the top, and there's low friction on the wheels/axles, so the car moves a little bit forwards and back as the gymnast swings. The forward motion is more or less equal to the backward motion, so the car does not go anywhere.)
  • What pattern did you observe in the car’s movement? (The car slows down in between each swing of the gymnast.)
  • Why does the car's travelling distance decrease between each swing? (The pendulum slowly loses momentum due to friction on the wheels and axles, as well as air resistance, so it will come to a stop with the pendulum at its lowest point).
  • What effect did a bigger swing of the pendulum have on the distance travelled? (The bigger swing generated more momentum, which made the car go farther.)
  • What did you observe when you released the gymnast with the car touching against your hand without the ratchet levers engaged? (There's an equal and opposite force, which you can feel as it presses against your hand when pushing off)
  • If the pupils are having difficulty answering, prompt them by asking:
    • Did you push it?
    • Then how did it move?

• If time permits, encourage your pupils to explore how they can make their car move backwards.
• Allow time for the pupils to disassemble their models, sort the bricks back into the trays and tidy up their workstations.

• Give feedback on each pupil's performance.
• Facilitate self-assessment.
• To simplify the process, you can use the assessment rubrics that have been provided.

Observation Checklist 

• Measure your pupils’ proficiency in describing how the mass of an object and the forces acting upon it can  change its motion.
• Establish a scale that suits your needs. For example: 
  1. Requires additional support
  2. Can work independently
  3. Can teach others

Self-Assessment 

• Have each pupil choose the brick that they feel best represents their performance. 
  • Green: With some help, I can describe how force and  mass can change an object's motion. 
  • Blue: I know I can describe how force and mass can change an object's motion.
  • Purple: I can describe  and explain how force and  mass can change an object's motion.

Peer Feedback

• Encourage your pupils to assess their peers by:
  • Using the brick scale above to score each other's performance
  • Presenting their ideas and giving constructive feedback

Model Tips

• It is common for pupils to make mistakes while building the gymnast’s arms (i.e. they build them backwards). If this happens, show them a completed model and point out the differences in construction.
• Remind your pupils that counting the holes in the beams and plates will help them to place the bricks correctly.

Simplify this lesson by:

• Having the pupils do only experiments 1 and 3, skipping the ratchets

Increase the difficulty by:

• Having the pupils figure out for themselves how to make the car move backwards, then repeating experiment 2 (They will have to fold in the front ratchet lever and lower the rear ratchet lever onto the gear.)
• Challenging your pupils to redesign the model to make it go farther, while still using the same brick weight as the pendulum mass

(Note: This will require additional time.)
To incorporate the development of maths skills, ask your pupils to experiment by pulling the gymnast back at 5 different angles with one of the ratchet levers engaged. Have them record the distance travelled from each angle. For an added challenge, ask them to plot the height from which the pendulum fell and how far the car moved on an x-y axis. Ask them to explain what the plot looks like and why.

ACMSP119
Construct displays, including column graphs, dot plots and tables, appropriate for data type, with and without the use of digital technologies

Download the Personal Learning Kit lesson plan from the hybrid learning resources.