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Work and Machines (Ch. 8)
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Gravity
In this chapter, you'll learn about work and how machines can help make work easier.
Terms in this set (36)
Work
This occurs when a force causes an object to move in the direction of the force. WORK does NOT occur if the object doesn't move or if the object DOES NOT occur in the direction of the force.
Joule
The unit used to express work.
Power
The rate at which work is done. Power tools do the SAME amount of work they just do it faster!!!
Watt
The unit used to express power.
Machine
A device that helps make work easier by changing the SIZE or DIRECTION of a force.
Work input
The work YOU do on a machine.
Work output
The work done BY the MACHINE. It is always less than the work input because of friction!
Mechanical advantage
This tells you how many times the machines multiplies force. It compares the input force with the output force. The higher this number is, the less force YOU have to input!
Mechanical efficiency
A comparison of a machine's work output with the work input. The less work a machine has to do to overcome friction, the more efficient it is. No machine is ever 100% efficient because of FRICTION.
Lever
A simple machine consisting of a bar that pivots at a fixed point called a fulcrum. (Ex. see saw, oars attached to a row boat)
Inclined plane
An inclined plane is a simple machine that is a straight slanted surface. A ramp is an example of a inclined plane. Advantage is you put less input force over a larger distance.
Wedge
A double incline plane that moves. (Ex. knife). The sharper/thinner/longer the knife the higher the MA!
Screw
A inclined plane that is wrapped in a spiral. Ex. basic screws that are used to hold things together, the tops of bottled waters, cokes (ie. a jar lid) Advantage is you exert a small input force, but over a larger distance!
Wheel and Axle
A simple machine that consists of two circular objects that are different sizes. (Ex. faucet, door knob, screw driver, anything that spins :) want a higher MA? make wheel diameter larger and axle diameter smaller (advantage is less input force, over a larger distance!)
Pulley
A simple machine consisting of a groved wheel that holds a rope or a cable. Rope segments that support the load = MA
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Verified questions
PHYSICS
You are an astronomer investigating four astronomical sources of infrared radiation. You have identified the nature of each source, so you know the frequency $f_{0}$ of each when it is at rest relative to you. Your detector, which is at rest relative to the earth, measures the frequency f of the moving source. Your results are given in the table. " $$ \begin{matrix}\text{Source} & \text{A} & \text{B} & \text{C} & \text{D}\\\text{f (THz)} & \text{7.1} & \text{5.4} & \text{6.1} & \text{8.1}\\\mathrm{f_{0}(\mathrm{THz})} & \text{9.2} & \text{8.6} & \text{7.9} & \text{8.9}\\\end{matrix} $$ " (a) Which source is moving at the highest speed relative to your detector? What is its speed? Is that source moving toward or away from the detector? (b) Which source is moving at the lowest speed relative to your detector? What is its speed? Is that source moving toward or away from the detector? (c) For source B, what frequency would your detector measure if the source were moving at the same speed relative to the detector but toward it rather than away from it?
PHYSICS
Two tiny metal spheres A and B, mass $$ m _ { A } = 5.00 g $$ and $$ m _ { B } = 10.0 g $$ , have equal positive charge $$ q = 5.00 \mu C $$ . The spheres are connected by a massless nonconducting string of length d = 3.00 m, which is much greater than the radii of the spheres. (a) What is the electric potential energy of the system? (b) Suppose you cut the string. At that instant, what is the acceleration of each sphere? (c) A long time after you cut the string, what is the speed of each sphere?
PHYSICS
A 60.0-pF vacuum capacitor has a plate area of $0.010 \mathrm { m } ^ { 2 }$. What is the separation between its plates?
PHYSICS
The “size” of the atom in Rutherford’s model is about $1.0 \times 10 ^ { - 10 }$ m. Determine (in eV) the electrostatic potential energy of the atom.
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