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prettybird

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  1. prettybird

    Lifting a Cat

    By prettybird,

    As you would know if you have a kitten, they only get worse as they age. This is intensely true for my kitten, Mia. Not only does she constantly escape her room, but she has figured out that my computer screen is touch screen, and wreaks havoc on whatever I am doing on the internet by touching it. 
    I often have to pick her up to try to prevent her from destroying something. She only weighs two pounds, even though she is 13-14 weeks old. I don't have to do much work because of her size, but there is still some being done. 2 pounds equals about .91 kilograms when converted. T-mg = ma would be the equation used to see how much tension is needed to lift her, however there is a flaw in using this equation, which I will discuss later. When I plug in the values, assuming I'm lifting her at a constant speed, the tension would need to be 19.6 newtons in my arm or 9.8 in each of my arms. (Back to the kittens being bad, as I wrote this exact sentence she climbed into my McDonalds bag and started licking my french fries. Kittens are like babies but they move faster and can't really be contained.) 
    But its unlikely I lift her at a constant speed, so lets say I lift her at an acceleration of 1.7 m/s2, just to change it up a bit. Then, when plugging the values in, the tension in one arm would have to be 23 N or 11.5 N in each arm. 
    Back to the problem with this equation. It assumes that the mass of the string (or arm in this case) is negligible, which obviously isn't true since my arms do have mass. This means that my values are off, but this is a high school blog so lets just forget about it for now and pretend my arms don't have mass. Alright, now that that's taken care of, have a nice day!
  2. prettybird

    Backpacks Part 2

    By prettybird,

    One comment I received on a previous blog about backpacks was about a backpack literally breaking your back. I decided to do some research on the topic. It appears that a vertebrae in your spine can withstand about 500 lbs of force, which is about 2225 N of force. In order to do some damage to your spine, you would need to have a backpack weigh this much in newtons. This means that your backpack would have to have a mass of 227 kg, or almost 500 lbs to do real damage to your back. 
    To put this in perspective, I estimated that a relatively full 2 inch binder is about 5 pounds on average. This would mean the backpack would have to hold about 100 binders to do damage.
    No only is it near impossible to fit that many binders in a backpack, and so you would have to have one specially made, but you would also have to have a group of people or even a small machine help you lift it onto your back in order to actually do the damage.
    Long story short, I don't think a backpack will be breaking your back any time soon.
  3. prettybird

    Ketchup Bottles

    By prettybird,

    I work at the bar, Murph's, on Friday and Saturday, and one of my tasks is to refill ketchup bottles. In order to get the ketchup to the neck of the bottle, I hold it by the bottom and spin it in a vertical circle. 
    This works because of centripetal force. You might be saying, however, that centripetal force pulls objects towards the center of the circle. While this is true, it acts on less dense materials at a greater magnitude. Inside the ketchup bottle, there is only air and ketchup. Since air is less dense, it gets pulled towards the center, displacing the ketchup. 
  4. prettybird
    There are several ways in which cars demonstrate physics. For one, when you turn, hit the gas or brake, you can see the property of mass called inertia. Anybody or anything in the car tends to continue traveling in the direction the car was originally going in or stay still if the car was stopped.
    Also, the physics behind tires show how cars move. As the tire spins, it uses the friction between it and the road to push the car forward. This is why in snow or mud, where there is little friction, the car cannot move.
    Finally, the antenna and speakers work together to receive radio waves from the air and transmit them into your car as audible sound waves.
  5. prettybird

    Falling Paper

    By prettybird,

    One thing I do on a daily basis is drop things. For example, pieces of paper or folders. When these things fall, they have the force of mg down, and the force of air resistance up. The paper will reach a terminal velocity and continue to fall at this velocity until it hits the ground. The force that the paper exerts on the floor is equal to the force the floor exerts on the paper. The coefficient of friction between the tile floor and the paper is likely small because the tile is smooth and the paper is also relatively smooth. This means that if the paper was acted on by some force, it would move easily across the floor. When I go to pick up the paper, since the paper's inertia is small, it is easy to pick it up. When I pick up the paper, I increase its potential energy (found by mgh) as I increase its height. When I set it back down on the table, the normal force from the table stops it from going through the table and opposes the force of gravity on the paper.

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