# Would a mouse trap snap faster or slower in space than on Earth?

Would a spring loaded mechanism outside a spacecraft activate a lever faster or slower in space with no atmosphere and gravity than on Earth?

Basically this is in reference to mechanical instruments or devices that are spring loaded and not for hydraulic or electronic devices. Especially in the event of a malfunction, a manual override would be in order.

• Wristwatches worn during Apollo missions are one example of spring loaded device not affected by space conditions – qq jkztd Mar 23 '19 at 7:32
• @qqjkztd what makes you say they are unaffected? To what degree is this known? Which astronaut has experienced the largest relativistic shift in time (relative to the surface)? – uhoh Mar 23 '19 at 8:01
• on Earth air resistance and gravity act to slow the trap (the trap spends more time accelerating upwards than downwards). In space the release mechanism has probably cold-welded, and temperature fluctuations may have done bad things such as annealing the spring - making it soft and unspringy; or hardening it, making it brittle and unspringy. – user20636 Mar 23 '19 at 8:26
• Unaffected in the way that relative to the astronaut who wears this watch, the spring behaves well enough to precisely tell time, regardingless spaceflight conditions – qq jkztd Mar 23 '19 at 9:06
• It would help if "in space" were better defined. Does it mean in a vacuum? Does it mean in free-fall? Does it mean exposed to solar radiation? etc. Strictly speaking, the Earth is "in space", as is everything in the universe. – Ray Butterworth Mar 23 '19 at 13:20

Would a spring loaded mechanism outside a spacecraft activate a lever faster or slower in space with no atmosphere and gravity...

Let's assume that faster or slower is in the local spacecraft reference frame so we don't have to worry about relativity.

The mousetrap (a reference to any spring-loaded mechanical actuation) will move very slightly faster without the drag force when atmosphere is present, all else being equal.

How much faster? The Instructables article Mouse Trap Speed! times it electrically and gives 12 milliseconds. If we ballpark the area and distance covered by the "business end" of the actuator at 100 mm^2 and 15 cm the average velocity is 12 m/s and use 1.2 kg/m^3 for the density of air $$\rho$$ and a drag coefficient of 1 in

$$F_D = \frac{1}{2} \rho v^2 C_D A$$

the drag force is about 0.01 Newton. I won't do the whole calculation but I think this will end up being a parts-per-million effect.

Of course "outside a spacecraft" the temperature is going to fluctuate wildly. Without atmosphere things can't effectively cool themselves so in the Sun the dark oxidized copper spring is going to get hot, and every time the satellite goes into the Earth's shadow it's going to radiate into space and cool very quickly. Thermal effects may change the energy stored in the spring and how rapidly it can release it due to internal friction within the metal's matrix. That's really hard to quantify.

Then there's issues of angular momentum. Is the mousetrap rigidly attached to the spacecraft or will it flop around by itself, these have different moments of inertia and so the angular acceleration will be different.

So it's quite a messy problem, but the only significant effect I can think of is the lack of aerodynamic drag. I don't see how being in microgravity will make much of an effect on the initial closing of the trap.

There seems to be some more detailed calculations on trap actuation here.

It can be faster.

A mouse trap: Consists of a rigid, heavy base plate and a piece of metal that is accelerated by a spring. The metal "arm" has to move by 180° between release and closing of the trap, first upwards then downwards.

Assume that the base is fixed to a heavy, rigid object and doesn't move when the trap is released. In this case the trap will close faster in space: During the first 90° of movement, the arm is accelerated upwards by the spring, but also has to counteract gravity. Depending on the ratio of the spring force and gravitational force, the arm is moving more or less slower than in the "space case" without gravity. The speed at the top point of the movement is therefore higher in space than on Earth and the total time to close is shorter. In the second half, gravity helps speed up the arm again, but this is not enough to make up for the time lost on the way up. In fact (if we ignore friction in air) the speed of the arm after the 180° movement is the same in space and on Earth, but the average speed is lower on Earth.