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  • 0 posts edited
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  • 11 votes cast
Dec
3
comment In terms of forces and kinematics, why does a projectile, thrown forwards, bounce forwards?
This video is also helpful youtube.com/watch?v=yS-n_1Zdtv4, you can see how the ball changes rotation everytime it bounces.
Dec
3
comment In terms of forces and kinematics, why does a projectile, thrown forwards, bounce forwards?
Yes, it starts slightly rolling forward. Depending on the lenght of the contact. You can slightly see it in the video, but you can observe it yourself. If you throw non-rotating ball on the ground, with some forward velocity, it will bounce with rotation.
Dec
2
comment Lift provided to an aeroplane
The Wikipedia article en.wikipedia.org/wiki/Lift_(force) is very detailed and provides very accessible explanation. It also has very good section on various misconceptions. From my experience, only minority of people who were explaining lift to me in the past got it right.
Dec
1
comment Can a wheeled vehicle remain stationary on a water surface?
I am afraid you question contains a lot of loopholes that offer several easy solutions and cannot be closed without ruining the question. For instance, you cannot really stay above water, at least some part of the vehicle has to be a bit sumberged, to be in contact. How much submersion do you allow? Why? Do you allow some fins or rotors attached to the wheels? Or what about if finned wheels spin so fast that the vehicle will essentialy almost fly above water thanks to redirected air? I think the answer is obviously yes. It is possible for stationary vehicle to remain on the surface.
Nov
30
comment Why we use liquid crystals in LCDs?
It does not. Have you seen the video?
Nov
30
comment Conservation of mechanical energy isn't giving me the right answer?
Mechanical energy is not conserved when there is a friction so you cannot use this method. You can verify it in simpler case: Suppose you pushed the package on a flat surface - its potential energy does not change, yet the package will lose kinetic energy as it will stop due to friction. Mechanical energy is not conserved - some/all of it will escape the system as heat.
Nov
26
comment Why is the gravity in a mine shaft independent of depth if the local density is 2/3 of the average density?
Can you cite a source? Assuming homogenous earth, gravitational acceleration decreases linearly with depth, with zero at the center of earth. I don't know what you call a "local density", but any density disturbances close to the shaft should not have a significant effect.
Oct
29
comment Error propagation with dependent variables
How do you compute $y_F$ ? Do you measure it by measuring $f(y)$ also for other values of $y$ and then compute the integral, or some other method gives you $y_F$ directly? Do you know the shape of $f()$?
Sep
4
comment Maximum reading after dropping a mass onto a scale
I think you are right that approximating scale just as a spring is unrealistic. This is because in fact it is heavily damped! When you step on the scale, it takes it only a few oscillations to stabilize. That means the first spike might be significantly lower compared to the undamped case. This however introduces new unknown quantity - damping constant, but I guess we would be able to estimate it if we measure the time it takes the scale to stabilize. By measuring frequency of the oscillations we can also improve our estimate of spring constant.
Jun
12
comment Accelerating a glass of a water across a table?
This is almost true, just that in the reference frame of the glass, the acceleration of the glass presents itself as inertial force in the opposite direction (the g is also equivalent to glass accelerating upwards, not downwards). So the picture is incorrect. Water level will be higher on the back side of the glass.
Oct
17
comment Rigid body dynamics joints
Sorry, I should've included the article name. It's "Advanced character physics" by Thomas Jakobsen. It's pretty well googlable.
Feb
20
comment Conservation of Energy and the Poynting Theorem
As I can't comment on the question above, I have to do it here: Dear ganzewoort, perhaps you should have commented here, rather than modyfying your question, thus disrupting the chronology of posts. As of the subject matter, you could have clearly read in my reply that I basically agree with you. Poyinting vector is rendundant in your sense. However, in the same sense the energy conservation law is also redundant, as it is fully derived from Maxwell equations, therefore states nothing new.