physics fun

[astroskeptic]

Say a missile (whatever kind you want) has a velocity of mach 3 if fired from the ground. It's on a plane traveling at mach 1. The pilot fires the missile, it leaves the plane at mach 4.
Correct?

Exactly. BTW, our understanding of these low-velocity situations is due to Isaac Newton, a genius who at the end of his life cited lifelong celibacy as his greatest accomplishment! (Einstein gave us understanding of high-velocity cases, i.e. near speed of light, and I'm not sure to what extent he share'd Newton's views on the merits of celibacy.)

Regarding the effects of panning, assuming you pan the camera at an even rate to match the apparent motion of the bike, I think you'd effectively return to the axle frame of reference in which all parts of the bike are motionless except for the tire, all points of which are moving at the same speed. So I'd expect uniform motion blur on the tire and no motion blur on the rest of the bike in a perfect pan.

 

[Josh66]

Regarding the effects of panning, assuming you pan the camera at an even rate to match the apparent motion of the bike, I think you'd effectively return to the axle frame of reference in which all parts of the bike are motionless except for the tire, all points of which are moving at the same speed. So I'd expect uniform motion blur on the tire and no motion blur on the rest of the bike in a perfect pan.

That seems to be the case, from what I've seen.

 

[Derrel]

Is there any need to consider the direction of the camera's shutter curtain travel when analyzing photos of an object moving at 25 to 30 miles per hour at close range?

Digital cameras do NOT expose the entire frame at the same moment....look for yourself and see how weirdly distorted helicopter blades can and do often appear when shot with a digital SLR...All available sizes | Mighty Low mmc | Flickr - Photo Sharing!

Who recalls this famous photo??? The picture linked to in the URL below, and the above modern photo, both show that photographs are not actually exposed "all at once", and so looking at a photo of a rapidly moving object shot with something as slow and clunky as an SLR Camera's shutter, and not a high-speed camera, can lead us astray sometimes...

Invincible Armor: Lartigue. One Of My Favorite Photographs

 

[clanthar]

Glad you all enjoyed that.

I'm no physicist either, but my son is; he's a physicist (Phd candidate) at U of Minnesota so I've had the figures that I posted with the tire verified -- not that I can explain it. I think astroskeptic has it. My son tries to explain it to me and I hear him say motion is relative to the frame of reference so what you see in the photo is from the camera's "non-moving" reference frame. When he goes on to insist that yes the bottom of the tire is stationary while the top is going 50 mph I get one of these too: Then he says, "look at your photo; what do you see?"

I'm a retired college professor with multiple graduate degrees (arts and humanities) and I'm not afraid of science, but that physics stuff..... So I have to tolerate my 25 year old patting me on the head and saying, "don't worry Dad, trust me."

Take Care,
Joe

 

[Infidel]

Is there any need to consider the direction of the camera's shutter curtain travel when analyzing photos of an object moving at 25 to 30 miles per hour at close range?

Digital cameras do NOT expose the entire frame at the same moment....look for yourself and see how weirdly distorted helicopter blades can and do often appear when shot with a digital SLR...All available sizes | Mighty Low mmc | Flickr - Photo Sharing!

Who recalls this famous photo??? The picture linked to in the URL below, and the above modern photo, both show that photographs are not actually exposed "all at once", and so looking at a photo of a rapidly moving object shot with something as slow and clunky as an SLR Camera's shutter, and not a high-speed camera, can lead us astray sometimes...

Invincible Armor: Lartigue. One Of My Favorite Photographs

I saw the helicopter photograph just the other day when I was reading up on what a rolling shutter was. Link:Rolling shutter - Wikipedia, the free encyclopedia