# Why can't a regular hammer be used in micro-gravity?

A comment under this question states that

"A good smack of a hammer" - is not a simple thing in zero gravity. You need a special hammer with absorption of inertia.

Why is this the case? Why is a special hammer needed, and what would this hammer look like? How would it work?

• Inertia. Elastic bounceback from a hit. Universe spinning around you after one hit, assuming you didn't also lose grip on the hammer. Vacuum rated gloves are not exactly dexterous. Commented Aug 25, 2021 at 13:50
• Even before the hammer hits, there'll be torque on your body due to conservation of angular momentum Commented Aug 25, 2021 at 14:07
• Try to imagine using a hammer while floating under water. Of course the target for the hammer is floating too. Experienced divers doing under water construction work know it.
– Uwe
Commented Aug 25, 2021 at 14:28
• @AntonHengst Underwater is easier because the water damps your motion (pun intended). Commented Aug 25, 2021 at 16:03
• @OrganicMarble agreed, but sadly I haven't found confirmation yet. My source was a colleague at Goddard almost 20 years ago, while we were standing next to and discussing the live electronic mockup of Hubble at GSFC, as opposed to the underwater non-electrified one in Texas. It might just be a story, but if so it was a good one. Commented Aug 27, 2021 at 19:43

To use a hammer in microgravity, you need to be firmly anchored to the object you wish to pound on.

Otherwise, you are at the mercy of action/reaction. As you swing the hammer, half of your effort will be spent moving the rest of your body back/around (it will be a complex motion counter to the swing of the hammer). Also, when the hammer hits, the force will be divided between pushing the item forward and pushing the hammer (and you) back. As a result, only a small amount of force is applied where you want it.

An alternative to anchoring yourself enough to compensate for all the messy angular forces, you can anchor the hammer. Picture a round clamp/magnet with a piston driven hammer in the middle. This would anchor the hammer without dealing with all the messy force vectors.

However, at that point where you are designing in hammer mounts for every nail, it becomes easier to design a different fastener type.

• Re, "when the hammer hits, the force will be divided..." The force between the handle and your hand should be much less than the force between the head of the hammer and the work piece. That's the whole point of hammers. If you could exert enough force with your hand to push a nail through a couple of 2x4s, then why would you need a hammer? When you swing a hammer, you build up it's momentum over something like a whole second by applying gentle force. Then ,when it hits, it decelerates in a few milleseconds (or sub-millisecond), thereby applying a huge force during that very short time. Commented Aug 25, 2021 at 23:42
• Yes, if the user is well anchored an ordinary hammer should work much like on Earth. Any manual work in microgravity starts with the user getting a firm hold (or being held) that allows leverage and prevents unwanted "equal and opposite reactions". Commented Aug 27, 2021 at 23:15

The current US EVA hammer is just... a hammer.

Source: EVA Tool Catalog

• On Mir, they used a type of dead blow hammer. There are a couple of Mir hammers on Ebay. (Sorry, I couldn't find a less commercial site with a decent image). Commented Aug 26, 2021 at 8:10