Prove the statement in Section 12.1 that the choice of pivot point doesn't matter when applying conditions for static equilibrium. Figure 12.28 shows an object on which the net force is assumed to be zero. The net torque about the point O is also zero. Show that the net torque about any other point P is also zero. To do so, write the net torque about P as τ → P = ∑ r → P i × F → i where the vectors r → P go from P to the force-application points, and the index i labels the different forces. In Fig. 12.28, note that r → P i = r → O i × R → where R → is a vector from P to O . Use this result in your expression for τ → P and apply the distributive law to get two separate sums. Use the assumptions that F → n e t = 0 → and τ → O = 0 → to argue that both terms are zero. This completes the proof. FIGURE 12.28 Problem 51
Prove the statement in Section 12.1 that the choice of pivot point doesn't matter when applying conditions for static equilibrium. Figure 12.28 shows an object on which the net force is assumed to be zero. The net torque about the point O is also zero. Show that the net torque about any other point P is also zero. To do so, write the net torque about P as τ → P = ∑ r → P i × F → i where the vectors r → P go from P to the force-application points, and the index i labels the different forces. In Fig. 12.28, note that r → P i = r → O i × R → where R → is a vector from P to O . Use this result in your expression for τ → P and apply the distributive law to get two separate sums. Use the assumptions that F → n e t = 0 → and τ → O = 0 → to argue that both terms are zero. This completes the proof. FIGURE 12.28 Problem 51
Prove the statement in Section 12.1 that the choice of pivot point doesn't matter when applying conditions for static equilibrium. Figure 12.28 shows an object on which the net force is assumed to be zero. The net torque about the point O is also zero. Show that the net torque about any other point P is also zero. To do so, write the net torque about P as
τ
→
P
=
∑
r
→
P
i
×
F
→
i
where the vectors
r
→
P
go from P to the force-application points, and the index i labels the different forces. In Fig. 12.28, note that
r
→
P
i
=
r
→
O
i
×
R
→
where
R
→
is a vector from P to O. Use this result in your expression for
τ
→
P
and apply the distributive law to get two separate sums. Use the assumptions that
F
→
n
e
t
=
0
→
and
τ
→
O
=
0
→
to argue that both terms are zero. This completes the proof.
Imagine you are out for a stroll on a sunny day when you encounter a lake. Unpolarized light from the sun is reflected off the lake into your eyes. However, you notice when you put on your vertically polarized sunglasses, the light reflected off the lake no longer reaches your eyes. What is the angle between the unpolarized light and the surface of the water, in degrees, measured from the horizontal? You may assume the index of refraction of air is nair=1 and the index of refraction of water is nwater=1.33 . Round your answer to three significant figures. Just enter the number, nothing else.
Chemistry: An Introduction to General, Organic, and Biological Chemistry (13th Edition)
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