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While theoretically present in all cases, most speeds that we can reach do not trigger effects that are measurable on a gross object. Therefore, any pendulum resilient enough to still exist after being hit by your rifle bullet will change momentum based on the simple formula of mass x velocity giving a number of foot-pounds or kg-meters or whatever system you are using, and the relativistic effects of something so slow as a rifle bullet will be very nearly too small to measure.
Here is the case that maybe will anchor some of this discussion. There is no absolute frame of reference, but there is an absolute limit for one thing - speed. Nothing in the physical universe travels faster than light.
One can argue that a particular photon could represent a frame of reference. The noticeable aging and mass effects predicted by the Lorenz-Fitzgerald (and related) equations only occur when you try to join the frame of reference of a photon that happens to be going in your desired direction. As you approach that frame of reference, your time dilation and mass accretion become significant. When you accelerate in the opposite direction from that photon (notice I did not say "decelerate"), your time flow becomes closer to other frames of reference that might even have people in them. They would see effects based on just how close you came to joining that photon's frame of reference. But YOU wouldn't see any effects at all until you rejoined a frame of reference where comparison became possible. (See? You can't get away from relativity because such comparisons are how you RELATE to something.)
Outside of the case of trying to join a photon, no other speeds make a significant difference, though long-term effects HAVE been measured for objects that reached orbital speeds, stayed that way, and then returned to frames of reference slower than the orbital situation. The more significant issue was that the returned objects were ALSO farther away from the frame of reference for photons.
I believe one of the objects in question was a digital clock or watch with a mechanism that counted vibrations of a quartz-based oscillator. There were predictable effects that included time dilation and mass inflation. Mass affects quartz oscillator vibration rates AND increased speed ALSO slows down apparent vibration rate, both of which were computable for the long-term conditions of being in orbit for a longer period of time. So we know that the effects are real.
If you can't wrap your head about the relativity issues any other way, here is your anchor point. Your speed with respect to cars, planes, boats, or trains is immaterial. The ONLY thing that noticeably affects is you is how close or how far you are from the frame of reference of photons that happen to be going in your direction. If you accept that the term "deceleration" only makes sense as "accelerating in the opposite direction from where I was originally pointed" then you can try to accelerate to the speed of light and can then decelerate from it. (But notice that "decelerate" only makes sense in RELATIVE terms, even as ACCELERATE only makes sense as relative to something else.)
Here is the case that maybe will anchor some of this discussion. There is no absolute frame of reference, but there is an absolute limit for one thing - speed. Nothing in the physical universe travels faster than light.
One can argue that a particular photon could represent a frame of reference. The noticeable aging and mass effects predicted by the Lorenz-Fitzgerald (and related) equations only occur when you try to join the frame of reference of a photon that happens to be going in your desired direction. As you approach that frame of reference, your time dilation and mass accretion become significant. When you accelerate in the opposite direction from that photon (notice I did not say "decelerate"), your time flow becomes closer to other frames of reference that might even have people in them. They would see effects based on just how close you came to joining that photon's frame of reference. But YOU wouldn't see any effects at all until you rejoined a frame of reference where comparison became possible. (See? You can't get away from relativity because such comparisons are how you RELATE to something.)
Outside of the case of trying to join a photon, no other speeds make a significant difference, though long-term effects HAVE been measured for objects that reached orbital speeds, stayed that way, and then returned to frames of reference slower than the orbital situation. The more significant issue was that the returned objects were ALSO farther away from the frame of reference for photons.
I believe one of the objects in question was a digital clock or watch with a mechanism that counted vibrations of a quartz-based oscillator. There were predictable effects that included time dilation and mass inflation. Mass affects quartz oscillator vibration rates AND increased speed ALSO slows down apparent vibration rate, both of which were computable for the long-term conditions of being in orbit for a longer period of time. So we know that the effects are real.
If you can't wrap your head about the relativity issues any other way, here is your anchor point. Your speed with respect to cars, planes, boats, or trains is immaterial. The ONLY thing that noticeably affects is you is how close or how far you are from the frame of reference of photons that happen to be going in your direction. If you accept that the term "deceleration" only makes sense as "accelerating in the opposite direction from where I was originally pointed" then you can try to accelerate to the speed of light and can then decelerate from it. (But notice that "decelerate" only makes sense in RELATIVE terms, even as ACCELERATE only makes sense as relative to something else.)
