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11-3-99
Sections 9.1 - 9.3
Objects in equilibrium
We've talked about equilibrium before, stating that an object is in equilibrium when it has no net force acting on it. This definition is incomplete, and it should be extended to include torque. An object at equilibrium has no net force acting on it, and has no net torque acting on it.
To see how the conditions are applied, let's work through a couple of examples.
11-1-99
Sections 8.7 - 8.9
Rotational work and energy
Let's carry on madly working out equations applying to rotational motion by substituting the appropriate rotational variables into the straight-line motion equations. Work is force times displacement, so for rotation work must be torque times angular displacement:
10-27-99
Sections 8.4 - 8.6
10-25-99
Sections 7.8 - 8.3
A 2-D collision
Momentum
There are two kinds of momentum, linear and angular. A spinning object has angular momentum; an object traveling with a velocity has linear momentum. For now, and throughout chapter 7, we'll deal with linear momentum, and just refer to it as momentum, without the linear.
10-18-99
Section 6.10
Power
Being able to do work is not just what's important; how fast you can do work is also an important factor. Power is the measure of how fast work is done. Computers have more calculating power than we do; a sports car generally has a more powerful engine than an economy car. Power is the rate at which work is done and the rate at which energy is used. The unit for power is the watt (W).
10-15-99
Section 6.9
With energy, we've got another tool in our physics toolbox to use to attack problems. Let's try some more examples to see how these energy concepts are applied.
Air resistance
Air resistance can be a tricky thing to account for. Generally, the force applied by air to a moving object is proportional to the square of the speed of the object. We know how to handle constant forces, but a force that depends on speed is a different story. If we apply energy to the problem, however, we can make some headway.
10-13-99
Sections 6.5 - 6.8
The conservation of mechanical energy
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