@Barbara_F wrote:
Please, dont' start that "arm movement/body movement" thing again.
Accelerometers measure velocity (speed) or vibration, not movement. This is why my One measured my steps on the bicycle, and my Blaze doesn't. There's less impact (vibration), and the Blaze has a different algorhythm But none of that is predicated on movement. It's velocity or vibration, not movement.
and I'll repeat, since people keep harping back to this arm movement thing, that most state of the art accelerometers use a triple-axis accelerometer, which measures three different axes to determine movement/impact.
https://en.wikipedia.org/wiki/Accelerometer
from the article: "It has been suggested to build football helmets with accelerometers in order to measure the impact of head collisions.[25]"
See the word "IMPACT"?
The Blaze is attached to your arm, so it does tend to make arm movements a factor. it's one of the reasons I got the One when I did. I wanted to avoid the limitations of a device that would subjected to random movements based on my arm motions. The One could be placed in a body neutral location. The Blaze cannot. But I upgraded because I wanted the heart rate, like I assume many others did.
Interesting when i search the link provided, the word Impact can not be found. An impact would cause a deceleration to zero real fast, and the speed (velocity) drops to zero. This would be considered negative acceleration.
From your link:
An eter at rest on the surface of the Earth will measure an acceleration g= 9.81 m/s2 straight upwards. By contrast, accelerometers in free fall(falling toward the center of the Earth at a rate of about 9.81 m/s2) will measure zero.
Velocity is speed, acceleration is the change in velocity. This can be caused by impact, or simply changing diredtion of travel. A train on a track going around a corner will be changing its foward velocity to a different angle. Some outward force, the rails, had an impact on the trains direction. Yes there was an impact, but it was a smoth impact, causeing a change in direction, a sidways vector or push. there was no bounce,l.
The One is not looking at the impact but the up/down motion of the body during a walk. The Blaze is looking at the forward and up/down motion of the arm during the walk.
The accelerometers is seeiing the change in velocity as the tracker switches direction.
Hold the tracker in your hand and move it smothly up/down. Don't make it stop fast at tye top or bottom of the cycle, their is plenty of velocity changing, with no impact of hitting the ground.
There is still impact but not the impact you are thinking off, for if your hand or gravity wasn't their the tracker would keep going in whatever direction it was going in.
This is what the Blaze sees the smooth changes in direction of the arm while walking..
BTW the NFL helmets have had accelerometers in them for a while now. Some high scholols have started using them, and now some elamentary schools are thinking considering their use.
When a head decelerates fast enough, as it would when being stopped by hitting the ground, are being forcibly pushed by another player, the second law of motion steps in, a body in motion tends to stay in motion, and your brain continues move until the skull changes its direction. The btain gets deformed as if it was a ball hitting the pavement.
Here is an interesting video on walking, with many shots of the body, head and arm movements.
The three axis accelerometer means that it is able to see changes in speed on the X,Y,an Z access. Their definately is an impact when your foot hours the ground, but their is none ehen gavity pulls the body down. While the arm has an impact on the movement of the Blaze it is not an impact as if the arm came in comtact with a stationary object.
As for why an object at rest on the surface of the Earth will measure an acceleration g= 9.81 m/s2 straight upwards. This can be explained in this video or web page. Gravity is the arm holding you on to the earth.
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