chap 4 – physics – Flashcards
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Which varies with location, mass or weight?
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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?
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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?
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Bottom string breaking = Mass
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State Newton's second law of motion.
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Acceleration is proportional to net force and inversely proportional to mass.
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How does acceleration depend on the net force?
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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?
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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?
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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?
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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?
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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?
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The force of friction is approximately independent of speed.
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Does fluid friction vary with speed?
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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?
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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 _____.
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Mass is kilograms; force is newtons.
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What is the approximate weight of a quarter-pound hamburger after it is cooked?
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One newton
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What is the weight of a 1-kilogram brick resting on a table?
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10 N
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How does acceleration depend on mass?
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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?
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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?
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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?
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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?
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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?
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The acceleration is in the direction of the net force.
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What is the condition for an object experiencing free fall?
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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?
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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?
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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?
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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?
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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?
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The force depends mostly on frontal area and speed.
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What is the acceleration of a falling object that has reached its terminal velocity?
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The acceleration is 0.
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Why does a heavy parachutist fall faster than a lighter parachutist who wears a parachute of the same size?
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Terminal speed must be higher to make air drag equal the gravity force for a heavier person.
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If two objects of the same size move through the air at different speeds, which encounters the greater air resistance?
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The faster object encounters more air resistance.
