SCEN final exam (discussion questions)

what is the meaning of quantity in physics

anything about an object that you can measure and describe using a number and a specific unit

alex says acceleration is how fast you go. Natalie says acceleration if how fast you get. They look to you for confirmation. Who’s correct and why?

natalie is correct because alex is describing speed. natalie is stating the rate at which speed changes (how fast you get), which is acceleration

in tearing a paper towel roll or a plastic bag from a roll, why a sharp jerk is better than a slow pull?

When you jerk the towel quickly, the roll’s inertia resists moving, so only one piece tears off. When you pull the towel slowly, the roll can start turning easily, so the towel just unwinds instead of tearing.

why is a massive cleaver more effective for chopping vegetables than a lighter knife that is equally sharp? explain

the massive cleaver tends to keep moving when it encounters vegetables, cutting them more effectively.

a common saying goes, “it’s not that fall that hurts you, its the sudden stop” translate this into newtons 2nd law

the sudden stop involved a large acceleration

why will a girl wearing gym shoes win in a tug-of-war against a boy wearing socks while the activity occurs on a smooth floor? explain

the gym shoes give more friction compared to the socks on the smooth floor, meaning that the girl would be able to exert more pulling force without slipping

why is it a good idea to have your knees bent when you land after a jump?

bending your knees after landing a jump increases the time that your momentum changes which minimizes the impact force

what does it mean to say a quantity is conserved?

its value remains constant over time

Freddy frog drops vertically from a tree onto a horizontally moving skateboard. the skateboard slows. give a reason for the slowing in terms of momentum conservation

no external forces act in the horizontal direction, since freddy’s mass is added, velocity must decrease

a pair of skaters initially push at rest against each other, so they move in opposite directions. A). what is the total momentum as the skaters push apart? B). is there a different answer if their masses are not the same?

A). the momentum is zero

B). each will have the same amount of momentum, but different speeds.

A). can something have energy without having momentum?

B). can something have momentum without having energy

A). yes, an object can have potential energy

B). no, any moving object must have both momentum and kinetic energy

how does this bulge affect the relationship between a person’s weight in singapore, and his or her weight in delaware?

the bulge of a person in singapore is farther from the earth’s center and therefore weighs less

newton tells us that gravitational force acts on all bodies in proportion to their masses. why, then, does not a heavy body fall faster than a lighter body?

the acceleration due to gravity is constant and does not depend upon the mass of an object

why do the passengers in high-altitude jet planes feel the sensation of weight while passengers in the space station do not?

the plane moves at about constant velocity, so a passenger experiences normal weight

does squeezing the ball increase its mass, or its density, or both?

squeezing the mall increases the density, but it’s mass will stay the same

why is blood pressure measured in the upper arm, at the end of elevation of your heart?

your upper arm is at the same level as your heart, so the blood pressure in your upper arms will be the same as the blood pressure in your heart

why do we have a water tower?

force of gravity acting on the water in a tall tower produces pressure in pipes below that supply many homes with reliable water pressure

lifting a baby underwater is easier to compare to when she is above the surface. explain?

a baby feels lighter in water because of buoyancy, which is an upward force exerted by the water that works against the baby’s weight

why do ships float?

ships float because the overall (apparent) density of the entire ship is less than the density of water

why does each donut have a white ring around the middle?

when the donuts float in the oil, only about 45% is in the cooking oil. when they are flipped over to cook on the other side, another 45% is cooked, leaving 10% as a white uncooked ring around the middle. archimedes principle

a partially filled flash of water rests on a scale. if you dip your finger into the water, without touching the flash, does the reading on the scale increase, decrease, or stay the same. explain

the reading on the scale increases, the upward buoyant force on your finger results in a downward force on the flask, which increases the reading on the scale

what is temperature?

temperature is a physical quantity that measures the degree of hotness or coldness of an object or substance, temperature is a measure of the average kinetic energy per molecule of a gas

what makes soda fizz? explain

when you open a soda bottle, the pressure inside drops, causing the dissolved carbon dioxide gas to expand & form bubbles, resulting in the fizzy effect

how do fish rise & sink in the water?

to rise, a fish must reduce its overall density by increasing its volume without significantly increasing its mass. fish can do this by filling the swim bladder with air

to sink, a fish releases the air in the swim bladder to reduce volume & increase its overall density

why will a helium-filled balloon rise in air while an air-filled balloon sinks?

a helium filled balloon rises because helium is 7 times less dense than air, meaning a helium filled balloon weighs less than the air it displaces, resulting in an upward buoyant force

an air filled balloon sinks because the air inside is denser than the air surrounding it, leading to a net downward force

what happens to a balloon when you let it go into the sky

as a helium balloon rises, the surrounding air pressure decreases, causing the helium inside to expand, and the balloon to stretch and increase in size until it eventually bursts

when passing an oncoming truck on the highway, your car tends to sway toward the truck. why? explain

Bernoulli’s principle. as the truck and car move closer, the air speed between them increases, causing a drop in air pressure in that area. this lower pressure area pulls the car towards the truck, resulting in the swaying sensation

why is an umbrella being in danger of being turned inside out on a windy day?

the fast-moving wind over the curved surface of the umbrella creates lower pressure than the slower moving air underneath, leading to a net upward force that flips the umbrella inside out. Bernoulli’s principle

why would you expect the molecules in a gas to have a variety of speeds?

gas molecules continually collide with one another, sometimes giving to and sometimes receiving kinetic energy from neighbors

why can’t you tell whether you are running a fever by touching your own forehead?

there would be no temperature difference between your hand and forehead. if your forehead is a couple degrees higher in temperature than normal, then your hand is also a couple degrees higher

which has the greater amount of thermal energy: an iceberg or a cup of hot coffee? defend your answer

the hot coffee has a higher temperature, but not a greater thermal energy. although the iceberg has less thermal energy per mass, its enormously greater mass gives it a greater total energy than that in the small cup of coffee

what is heat?

heat is energy transferred from one body to another because of a difference in temperature

desert sand is very hot in the day, and very cool at night. what does this tell you about its specific heat capacity? explain

sand has a low specific heat, as evidenced by its relatively large temperature changes for small changed in thermal energy

why does jello stay cooler for a longer time than sandwiches when both are removed from a picnic cooler on a hot day?

water in the jello has more “thermal inertia” a higher specific heat capacity than a sandwich ingredients

why are power lines sagging?

power lines sag due to thermal expansion and to allow for safe tensions, prevent breakage under varying conditions

in terms of thermal expansions, why is it important that a lock and its key be made of the same materials

for a lock and key to function reliably, they should be made out of the same or similar materials because different materials expand and contract at different rates which temp changes, which can lead to a poor fit and difficulty in operating the lock

what is the purpose of copper or aluminum layer on the bottom of a stainless-steel pot

copper and aluminum are better conductors than stainless steel, meaning they transfer head more quickly and efficiently

is snow a good insulator or not?

yes snow is a good insulator because it contains a lot of trapped air, which slows down heat transfer and acts like a blanket, helping to keep the ground

many tongues have been injured by licking a piece of metal on a very cold day. why would no harm result if a piece of wood were licked on the same day

metal, a conductor, pulls heat away so quickly so that your saliva freezes almost instantly so your tongue sticks to the metal

wood, an insulator, transfers heat much slower, so your saliva stays liquid

from a physics standpoint, what is the main reason for sweating?

people sweat, primarily to cool down their bodies triggered by factors like heat, exercise, or emotional stress

why does wrapping a bottled beverage in a wet cloth at a picnic often produce a cooler bottle than placing the bottle in a bucket of cold water?

when water evaporates, the hottest molecule leaves first which lowers the average energy of the water left behind, making it cooler

why do dogs pant?

dogs have no sweat glands, so they pant. when they do pant, they rapidly inhale and exhale air, increasing the evaporation of moisture from their tongue and respiratory system

why do people breath heavily after physical activity

when we exercise, our muscles require more energy and therefore more oxygen, when humans pant, they increase their breathing rate to get more oxygen into the blood and remove excess carbon dioxide, a waste product of energy production

why is a stem burn more damaging than a burn from boiling water of the same temp?

when boiling water reaches 100C, it requires additional energy to become steam, when it touches skin, it cools down and condenses back into the boiling water which releases extra heat into the skin

does spaghetti cook faster in vigorously boiling water than in gently boiling water?

vigorously boiling water does not reduce the cooking time because it is only to ensure that the spaghetti doesn’t stick to the pot

discuss why half-frozen fruit punch is always sweeter than completely melted fruit punch

in the half frozen punch, the water turns into. ice, but the sugar and flavor stays unfrozen which leaves the remaining liquid more concentrated with sugar