Question:

Can you explain why the pile driver exerted a smaller impact force on the quail egg when the impact is cushioned?

Answer:

With cushion, the pile driver is brought to rest less quickly.

This means that the same change in momentum (Δp) is achieved over a longer duration of time (Δt), which implies a smaller impact force on the pile driver according to Newton’s 2^nd Law (F=Δp/Δt)

By Newton’s 3^rd Law, the impact force on the egg is also smaller.

Delving deeper

The slow-mo replay shows clearly how the cushion, being soft and yielding, allows the egg to back away slightly from the incoming pile driver. This is crucial in extending the impact duration. In fact, the slow-mo replay shows that the impact duration was almost doubled (29.1 ms compared to 16.7 ms). This tells us that the peak force experienced by the egg was roughly halved because of the cushion.

We can also sketch the F-t graphs for both cases.

With cushion, the force is about halved because the duraction is about doubled. However, both graphs have the same area. This is because the area under an F–t graph represents the change in momentum.

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