# Chap 4 - Physics

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question
Which varies with location, mass or weight?
Weight varies with location, but mass does not.
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In the string-pull illustration in Figure 4.8, a gradual pull of the lower string results in the top string breaking. Does this occur because of the ball's weight or its mass?
Top string breaking = Weight
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In the string-pull illustration in Figure 4.8, a sharp jerk on the bottom string results in the bottom string breaking. Does this occur because of the ball's weight or its mass?
Bottom string breaking = Mass
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State Newton's second law of motion.
Acceleration is proportional to net force and inversely proportional to mass.
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How does acceleration depend on the net force?
Acceleration is proportional to the net force.
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When you push horizontally on a crate that doesn't slide on a level floor, how great is the force of friction on the crate?
The friction force is equal and opposite to your push.
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As you increase your push on a stationary crate, will friction on the crate increase also?
The friction force increases and is opposite in direction to your push.
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Once the crate is sliding, how hard do you push to keep it moving at constant velocity?
You push with a force equal to and opposite the dynamic friction force.
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Which is normally greater: static friction or sliding friction on the same object?
Static friction is normally greater than dynamic friction.
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How does the force of friction for a sliding object vary with speed?
The force of friction is approximately independent of speed.
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Does fluid friction vary with speed?
Fluid friction increases as speed increases.
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Shake something to and fro and you're measuring its what? Lift it against gravity and you're measuring its what?
Shaking measures mass, whereas lifting measures weight.
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Fill in the blanks: The Standard International unit for mass is _____. The Standard International unit for force is _____.
Mass is kilograms; force is newtons.
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What is the approximate weight of a quarter-pound hamburger after it is cooked?
One newton
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What is the weight of a 1-kilogram brick resting on a table?
10 N
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How does acceleration depend on mass?
Acceleration is inversely proportional to mass.
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Give an example of what it means to say mass and weight are proportional to each other?
If the mass doubles, then the weight doubles, too.
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If the net force acting on a sliding block is somehow tripled, what happens to the acceleration?
The acceleration triples.
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If the mass of a sliding block is tripled while a constant net force is applied, by how much does the acceleration change?
The acceleration is reduced to 1/3 of its original value.
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If the mass of a sliding block is somehow tripled at the same time the net force on it is tripled, how does the resulting acceleration compare with the original acceleration?
The acceleration remains the same.
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How does the direction of acceleration compare with the direction of the net force that produces it?
The acceleration is in the direction of the net force.
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What is the condition for an object experiencing free fall?
When gravity is the only force acting on an object, it is in free fall.
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The ratio circumference/diameter for all circles is π. What is the ratio force/mass for freely falling bodies?
The ratio is g
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Why doesn't a heavy object accelerate more than a light object when both are freely falling?
The ratio of the weight to mass is the same for all objects in the same locality.
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What is the net force that acts on a 1-kg freely falling object?
10 N
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What is the net force that acts on a 10-N falling object when it encounters 4 N of air resistance? When it encounters10 N of air resistance?
The net forces are 6 N and 0 N, respectively.
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What two principal factors affect the force of air resistance on a falling object?