Teaching Sequence

Work through this resource material in the following sequence:

30 minutes

Part A: Modelling a fall

25 minutes

Part B: Head injuries

5 minutes

Reflection

Part A: Modelling a fall

Step 1

Explain to students that, following from the last lesson, where they looked at the forces acting upon someone when punched, they are going to be investigating the effect of the fall on a person’s head. They’re going to do this by dropping different balls onto different surfaces and observing the differences between the balls landing on both surfaces.

In the experiment, the balls being dropped will be:

a basketball
a medicine ball (the weighted type typically found in a gym)
a third ball of a different type (optional), chosen by you or the class. Alternatively, a sandbag of similar size might be an interesting option because it will much more easily deform to absorb the impact, unlike the other two. If you want to get messy, a watermelon would also be a reasonable analogy (melons are often used in tests as a head replacement), but it’s worth keeping in mind that the smashing of a melon could be triggering for students, given that there might be connotations of a head being broken in a similar manner.

These balls/objects will be dropped on two (or more different surfaces). We suggest concrete and grass to give a very clear difference in terms of reducing the impact via cushioning or elasticity.

So that it’s easier for students to remember the variables being altered in the experiment, we recommend you write the details of ball and surface types on the board.

Step 2

Having established the outline of the experiment, ask students to come up with a suitable aim and hypothesis for the experiment, using the conventions they should, hopefully, be familiar with by now. In this lesson, we really want to focus on the experimental outcomes so, if time permits, you can spend some time revising aims and hypotheses-writing, but if time is of the essence, don’t feel the need to dwell on the aim and hypothesis too much at this stage.

Step 3

Choose a suitable location for dropping the balls (inside your classroom is probably fine, although this can be a nice chance to get your class outside).

Ask student volunteers to hold the balls at the same height, give them a countdown and have them drop them at the same time. Have the students complete the see, think, wonder table on their worksheets. Be clear with students that they are only to drop, not throw, the balls at the ground, as this can be dangerous (for students, observers and any fragile objects in the area) and affect the results.

Step 4

Try and get the class to determine why one ball bounced quite a bit higher than the other, as well as what made them fall. Here are some sample questions (and answers) ranging from easiest to hardest - choose the questions most suitable for your class:

Force questions:

Which force caused the balls to fall?
The force due to gravity.
What is gravity?
The force of the Earth’s mass pulling other masses towards it.
Were there any forces acting against the movement of the ball?
Yes, air resistance.
Which ball had the larger force acting on it?
The heavier one.
What did you notice about the time that they hit the ground?
They hit around the same time.
Why didn’t the ball with more force (or mass) move faster than the other?
Inertia - heavier things take more force to accelerate.

If you want to explore how the shapes of the balls change when dropped, ask if any students have a camera capable of slow-motion video recording on their phone and ask them to record the impact. The slow motion should allow you to see in greater detail how the balls deform on impact and there’s a reasonable chance that there is at least one student with slow-motion recording capabilities. Ideally, they’ll record both balls hitting the ground for comparison. You might like to refer to these resources for support:

Step 5

Repeat this process, but by dropping just the basketball on two different surfaces (i.e. concrete and grass, brick and sand, etc.; any sufficiently different surfaces will do). Perform the drops and get the students to see, think, wonder, then draw out the concepts using this comparison:

Between the drop on the hard surface and the drop on the soft surface, what things stayed the same and what things changed?

Stayed the same:

conditions: starting height, wind conditions, temperature
the ball: mass, size, shape, texture, internal pressure
forces: force due to gravity, downward acceleration, air resistance value
energy: initial gravitational potential energy, kinetic energy (speed) as the ball hit the ground.

Changed:

conditions: the surface of the ground
energy: more energy was 'use'” in changing the ground (squishing soft dirt or grass, moving sand particles etc.) and so less of that initial energy was available to provide kinetic energy (movement) of the ball back up.

Step 6

Have the students draw a simplified force diagram for a basketball falling on concrete on their worksheets. Go over solutions on the board when you are ready. They are given below for your convenience.

The following activities might be challenging or triggering for some students. Refer to the Handling Sensitive Topics and Issues Factsheet and allow students to step out or take a break (or anything else they need to do to take care of themselves) as needed.

Step 7

Ask the students if they think the human head would behave more like the basketball or the medicine ball. Since it doesn’t bounce like the basketball, what implications does this have for the magnitude of the force applied to the skull - how might the skull, or the brain, respond to such forces? Also, what do they think the difference is for someone falling on concrete versus grass or another, softer surface?

The internet is awash with recorded fights or assaults where a victim is knocked over or is unconscious after the punch before falling onto a hard surface and this is oftentimes the most deadly part. Massive deceleration when hitting the ground causes almost all of the force to be applied to our head in a very short space of time and this is deadly. By changing the drop surface, we can show that softer surfaces will reduce the impact on the head and cause less injury. Additionally, we’re demonstrating to students that the vast majority of the force of the fall is absorbed by our head and it is this force that causes the most significant damage, not the initial blow to the head that caused the fall. This is a perfect time to remind students to always wear a helmet, and wear it properly when on their bike, skateboard or scooter: helmets absorb the impact that would otherwise be transferred to our skull. It’s better to 'look silly' than it is to be in the hospital with head injuries.

As the brain is inside our skull, we often think of it as being static or fixed in position, but this is not the case. In a collision, the brain will continue to move in the same direction as the rest of the head until an unbalanced force is applied to it. In this case, it will be the skull pushing back in the opposite direction once the head hits the ground. To conceptualise this, ask students to consider what happens when they’re in a car that brakes suddenly: they continue moving forward until the seat belt pulls them back into place. In a fall, our brains will act like the body in a car and the skull acts like the seatbelt.

Part B: Head injuries

If time permits, you may wish to start the following activity in class or assign it as a homework task.

Be sensitive to the emotions of your students from the preceding activities to determine whether or not this is an activity you wish to have students work on without supervision, as the theme of the content may be triggering for some.

Step 1

Ensure each student or small group of students has access to the Medical Effects Of One Punch Article.

Step 2

Individually or in small groups, ask the students to read the article and answer the questions and prompts found on their worksheets. The solutions can be found below for your reference. The original website also contains the following 1-minute video about the coward punch that you may wish for students to view:

It just takes one punch (https://www.youtube.com/watch?v=TPotAZ1KuWs)

This activity can also be linked back to what students already know about body systems, and also as a precursor to what will be covered in Year 9.

Who published this information, and in what year?
The Queensland Government, in 2017.
What happens when the brain 'rattles' inside the skull and how does this cause serious medical effects?
Like jelly being shaken, the connections within the soft brain tissue (the neurons) can be damaged and broken. This trauma can cause various medical conditions.
Draw a force diagram to represent what happens when the brain 'rattles' inside the skull.
List five serious possible outcomes of this kind of brain trauma
Concussion, damage to the brain stem, skull fracture, brain swelling, haemorrhage and hematoma.
What is the brain stem responsible for?
Regulation of breathing, heartbeat and digestion.
Think: What might some consequences be if the brain stem was damaged?
Autonomic systems may not function correctly, you may have trouble breathing, complications in the circulatory system and digestive systems or death.
After blood supply to the brain is lost, how long does it take for the following to occur?
- Unconsciousness - 8 to 10 seconds
- Brain damage - 4 to 6 minutes
What do surgeons have to do to relieve swelling of the brain?
Drain the fluid from the skull or remove a piece of the skull.
What is a hemorrhage?
Excessive bleeding.
What are some of the possible lifelong effects of the type of damage caused by coward punch attacks?
Many possible answers, including:
- Inability to work or study
- Psychological problems
- Inability to perform basic daily tasks
- Disability
- Death

Reflection

Ask students to offer insight on what they learned today and what today’s lesson made them wonder about (there are prompts on the Student Worksheet if you want them to record these thoughts).

You may wish to offer students the chance to provide feedback on the lesson or ask any outstanding burning questions they have about it.

Learning extension: Advanced students can investigate further into air resistance. Ask them why a hammer and a feather fall on Earth at different rates, while on the moon they fall at the same rate. They don’t believe you? Here is the footage:

Hammer vs Feather - Physics on the Moon (https://www.youtube.com/watch?v=KDp1tiUsZw8)

Have them watch this and write a see, think, wonder table. Ask them to think about what is the same about Earth and the moon and what is different, and write these things in dot point lists. If possible, this would work best in pairs or small groups so students can debate and discuss. Ask them to guess why this experiment works differently on the moon than it does on Earth.

Have them watch the solution here:

Danger! Falling Objects: Crash Course Kids #32.1 (https://www.youtube.com/watch?v=dxcx35x5L9Y)

Have them answer the question, in their own words: Why do a hammer and a feather fall at the same rate on the moon but not on Earth?

Coward Punch - Modelling the Forces of a Fall

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