# What happens when 2 shock waves collide?

• pyroknife
In summary: That's a great question. The combined speed would be the sum of the speeds of the two shocks, which would be 2+1m/s.

#### pyroknife

If I have 2 shock waves propagating at different speeds in a tube, let's say to the right.
Let's say initially one of the shocks (shock 1) is ahead of the other (shock 2), but shock 2 is faster than shock 1, so eventually shock 2 will catch up to #1. What happens when they catch up? Do they become one shock?

Is it possible to get two shockwaves to propagate at different velocities in the same tube? Just curious as to how you might do that.

It is definitely possible to get two shock waves to propagate and different velocities in the same tube. Consider a tube with three regions of different pressure separated by two diaphragms arranged in order of decreasing pressure. Let's say they are arranged from left to right as ##p_3##, ##p_2##, ##p_1## and ##p_3>p_2>p_1##. If you pop both diaphragms at the same time and the pressure ratios across each are sufficiently high, you can start two shocks in the same tube. Assuming the two shocks are of equal strength (pressure ratio), they will have the same Mach number but the trailing shock will be traveling through a medium with higher sound speed and therefore will eventually catch the leading shock given enough time. So the answer is yes, it is possible to do and it depends on the shock strength of the two shocks. If you made the trailing shock sufficiently weak, it would never catch up or even fall behind.

The problem with just talking about interference is that superposition only works for linear phenomena. Shock waves are, by their very definition, nonlinear, so simple superposition does not hold like that. Instead what would happen (if I recall correctly) is that the second shock would catch the first and the two would essentially merge into a new, stronger shock. After all, the first shock had a pressure ratio of ##p_2/p_1## and the second shock would have a pressure ratio of ##p_3/p_2## when it gets close to the first shock, so right when they touch, the ratio across the combined shock would then be ##p_3/p_1##. This simply represents a stronger shock.

Danger
Thanks! What if the lagging shock was travleing at say 2m/s and the leading @ 1m/s. When the lagging shock catches up and collides with the leading shock, does stronger shock travel at a combined speed of 2+1m/s?

## 1. What is a shock wave?

A shock wave is a type of propagating disturbance that travels through a medium at supersonic speeds, causing a sudden and drastic change in pressure, temperature, and density. It is typically generated by a sudden release of energy, such as an explosion or a high-speed object moving through the medium.

## 2. How do shock waves behave when they collide?

When two shock waves collide, they interact with each other and produce complex patterns of compression, rarefaction, and reflection. The resulting behavior depends on the strength, speed, and direction of the shock waves, as well as the properties of the medium they are traveling through.

## 3. Can shock waves cancel each other out?

In theory, it is possible for shock waves to cancel each other out if they have equal strength and are traveling in opposite directions. However, in practice, it is difficult to achieve perfect cancellation due to various factors such as shock wave interference and energy dissipation.

## 4. What happens when two shock waves with different speeds collide?

If one shock wave is significantly faster than the other, it will overtake and compress the slower shock wave. The resulting shock wave will be a combination of the two original shock waves, with a higher amplitude and a more complex structure.

## 5. How do scientists study the collision of shock waves?

Scientists use various experimental and computational techniques, such as high-speed photography and numerical simulations, to observe and analyze the collision of shock waves. These methods allow them to capture detailed information about the shock wave behavior, such as pressure and temperature changes, and study the underlying physical processes involved.