Unit 3: FORCES

In Unit 3, we learned about forces. What happened to Newton? Well, his third law was a big part in this unit.

Newton's Third Law

His third law states that every action caused upon an object, or is caused by an object, has an equal and opposite reaction. What does this mean? Well, when you are walking forward, you push the ground behind you; push is a type of force. This force and action has a reaction to it which is the ground pushes you forward. To have a real action and reaction pair, the force has to be the same between the same objects. In this action and reaction pair, the forces are equal, which means if you were showing a picture, the vectors will also be equal. Here is an example with a horse pulling a cart (Sorry for the bad writing):

As you can see, The vectors for the horse and ground using one another are similar to the size of the horse and cart pulling one another. This is because they're similar forces, but you see the cart and ground pushing vectors are smaller than both is because the cart isn't really causing itself to push the ground, it's being pulled by the horse, so less force itself. 

Perpendicular Forces

In the above, I wrote about how parallel forces are there and now what about what happens when you are in a boat sailing to cross a river thats flowing a certain speed. Let's say the river flows 5m/s down and the wind pushes you about 3m/s. Here is an example: 

Here, since the rive flows down 5m/s and you sail across 3 m/s, your boat will go at an angle 4m/s, until you hit the x. We know it's 4 because of our 3-4-5 right triangles. These forces and actions happen in everyday life such as boat in a river or a plane with wind pushing it.

Tides

In this unit, we also learned about tides. Tides happen everyday on Earth. We experience 4 tides a day, 2 high and 2 low. Each high and low tide are 6 hours apart from each other, so that means each high tide is 12 hours apart, same for low tides. What causes these tides is the force of pull from the moon. The moon pulls the water and Earth towards it, but the Earth fights back, kind of like tug of war. The formula/equation we use to show the force of gravity is F=G(m1m2/d^2). G is 7*10^24 (or near that).Since the Earth pulls back to stay in its orbital, it causes the tide bulge, which is the oval water shape. If the moon pulls the water closest to it/ the side of Earth facing it with let's say 5N, then the other water side is being pulled with -5N because of this tug of war. Negative is a force in the other direction. This means that if theres a high or low tide on one side of the earth, then it's the same on the opposite side. Tides are caused by the phases of the moon and sun. When the sun and moon line up with he earth in somewhat a straight line, those are called spring tides, when the tides are higher then usual. When the moon is on one side of the earth and the sun is on the other side, 90 degrees, this forms neap tides.

Momentum 

Last thing we learned about was momentum. Momentum in physics variables is p, and p=mass(velocity) [p=mv] measured in kgm/s. We learned that when an object that's moving hits another object thats at rest, gives/passes its momentum through it and moves/sticks together and moves together at a new velocity. Same momentum? Yes, because the momentum before is equal to the momentum after. Also, if there was a change in momentum on an object, to find this change you would use the final momentum minus the initial/starting one. This leads to the impulse on objects too. Impulse is the variable J. J= the change in momentum and it also equals force times the change in time. This is measured in Ns. Law of conservation momentum is showing the relation momentum and impulse. All of this helps us figure out why gymnast use matts instead of the hard floor to land on, the matts slow them down (longer time), so small force, and small force causes less injury. This also shows us why we don't have rubber bumpers on cars, land with bent knees, and landing in snow can help us survive off a mountain.

How Tides Work

Here I have found a video/resource to explain tides in an animated way.
Tides happen everyday on Earth. We experience 4 tides a day, 2 high and 2 low. Each high and low tide are 6 hours apart from each other, so that means each high tide is 12 hours apart, same for low tides. What causes these tides is the force of pull from the moon. The moon pulls the water and Earth towards it, but the Earth fights back, kind of like tug of war. Since the Earth pulls back to stay in its orbital, it causes the tide bulge, which is the oval water shape in the video. If the moon pulls the water closest to it/ the side of Earth facing it with let's say 5N, then the other water side is being pulled with -5N because of this tug of war. Negative is a force in the other direction. This means that if theres a high or low tide on one side of the earth, then it's the same on the opposite side.
Tides are caused by the phases of the moon and sun. When the sun and moon line up with he earth in somewhat a straight line, those are called spring tides, when the tides are higher then usual. when the moon is on one side of the earth and the sun is on the other side, 90 degrees, this forms neap tides.

http://www.tide-forecast.com/locations/Grand-Cayman-Cayman-Islands/tides/latest

Here are the tides of the Cayman Islands, the main island, Grand Cayman. Grand Cayman experienced high tide, going down to low tide when I wrote this. These tides/this beach is going to experience spring tides in the next few days, since it's going to be a new moon. So they are getting ready for those high and low tides.

Newton's 3rd Law

In this video, this guy explains Newton's third law. This 3rd law is every object that has an action also has a reaction. This means if the earth pulls me, I pull the earth too. Another example is an apple in my hand. I push the apple up and it pushes my hand down.
This video the guy explain more examples of how it's all connected. It's a really great video to go by and helps if you ever need help in this area of Physics. He explains the law, shows examples of most-all action and reaction pairs, with their vectors. Vectors are the arrows you see in the examples that show which way or how much of the force is happening in a certain direction. If you need more help with the 3rd law just watch this video!

Newton's Second Law Review (UNIT 2 REVIEW)

In Unit 2, I learned about Newton's second law. This law talks about the relations with force, acceleration, and mass. Acceleration has a verse relationship with force, but an inversely relationship with mass. If force is increased then acceleration increases, if mass increases then acceleration decreases, and vice-versa for both. Many people get this confused with the actual definition of acceleration, a=change in velocity over time, these relations are just proofs for the second law.
 I also learned about free fall, free falling at an angle, free falling when thrown up, and skydiving fall (fall with air resistance). Let's start with Free Fall basics.

Free Falling

In Free Fall there is no resistance. What does that mean? Well, no air resistance means like you're in space, where if you moving/falling nothing (no air) is being pushed against you, this means you fall at a constant acceleration.

For the constant acceleration of free fall, we use a=9.8m/s^2. Most of the times, like in labs we used a=10m/s^2. So every second, you increase your speed by 10m/s (9.8).

Last bit to remember mostly about free fall is weight/mass does not matter. If you had no air and dropped a feather and a brick, they would hit the ground at the exact same time.

Free Falling @ an Angle

So, have you ever heard about a plane that needs to drop a package, or you jumping off a cliff. Well, where do you/the package land, how long are you/the package in the air for. We can calculate all of this using d=1/2gt^2 and d=vt.

To find the time, use the height (vertical) distance to see how long it would take you to get to the ground. Let's say you were on a 250m high cliff and wanted to figure out how long it will take you to hit the ground, if you ran off at a constant speed of 5m/s. d=1/2gt^2 is the equation we will use, so 250=1/210(t^2), 250/5=t^2, 50=t^2, t=7.07 seconds.

Now that you have seconds you can see how far you will go too. d=vt is the equation we use for horizontal distance. Plug it in (d=5(7.07)), you will go 35.35 meters. To find the actual velocity you are going at any second, use a triangle, and see how to do the other things like so:

Special triangles are the right triangles in which we use the 345, and a^2+b^2=c^2

Free Falling When Thrown Up

Now we have a ball thats thrown up. You can see how, since there is still no air resistance, the ball will decrease in acceleration up by 10m/s^2 and increase on its way back down. 

To find the height, use the d=1/2gt^2, to find the total height of its highest part. Once you find this, you can use the same equation to find how high the ball is after 3s, 5s, etc.. Just use the same equation and then subtract it from the total height.

Also to do with an angle thrown, here is another video made by my friends to explain it better: 

Falling (Sky-Diving)

Unit 1 Review

In this first unit, I learned many things. I learned about force with Newton's first law and how to apply it in everyday life, like I did when I rode the hover craft, net force, and equilibrium, all of these are subtopics of Inertia. I also learned about constant velocity, constant acceleration, and how to use the equation of a line (a graph) to solve problems for both of these topics.

Inertia

In this area of the unit, I learned about Inertia and force. Mass is the measure of Inertia, in kilograms. 

Force is either a push or a pull, and it's measured in Newtons (N), which equals 1/4 of a pound. An object that is being pushed with 5 Newtons to the left, that object will be moving to the left, and have a net force of 5 N to the left. Whenever you have forces on opposite sides of an object, you subtract both sides Newtons from each other to find the total net force. If the forces are on the same side, you add them. Another example of an object with force is the hovercraft; the hovercraft was at constant velocity, meaning it never sped up, slowed down, or changed direction, and the net force was 0 N. If something is at constant velocity and/or have 0N, it's at a stage called equilibrium. This object could be at rest or moving at a constant velocity.

Another thing in Inertia I learned was the force of friction. If friend A pushed a box that's at rest with 100N and it didn't move, what is the force of friction? The force of friction would also be 100N because to stay at rest/equilibrium, the box would have to equal a total amount of 0N (100N-100N=0N)
One of the big things we learned in Inertia is Newton's first law. His first law is: an object in motion/rest, tends to stay in motion/rest unless acted upon an outside force. A big question I always received was; I left my coffee on the trunk of my car, when I took off it falls to the ground at the exact spot it was above the ground on my car trunk, why? The answer is that the coffee is at rest on my trunk, so when I take off, the force under it (the car) swipes from under it, not strong enough/too fast to keep it on the trunk, leaving the cup to fall right there. This explains Newton's first law of an object at rest tends to stay at rest unless acted upon another force. The coffee was the object at rest, and the car moving from under it was the weak/fast force. Another example is this graduated cylinder skateboarding:

Here the rock (outside force) stops the skateboard (the object in motion), and causes the graduated cylinder to keep on moving, because the rock wasn't big enough to stop him too.

Speed & Constant Velocity

Speed is the movement of an object at a pace that's fast or slow. I learned that constant velocity is going at a certain speed the whole time through the process. Constant velocity relies on 2 things: 1. constant speed. 2. One certain direction. This means that if you speed up, slow down, or turn, you will not be in constant velocity. I learned that to measure velocity it's meters over seconds (m/s). We measure velocity by the distance over the amount of time (v=d/t). Objects can be at a constant speed, and sometimes at a constant velocity, because they could be turning, but if they weren't then they are at constant velocity. Constant velocity has certain formulas to find the distance and speed for when an object has constant velocity. The distance equation is: d=vt, and the speed formula is the same as the constant velocity one which is v=d/t.

An example of constant velocity is me driving my car. I drive my car for 5 seconds and went 600 meters, how fast was I going? Well, if I use the constant velocity formula, v=d/t, I can plug in 600 for d, and 5 for time, and get 120m/s. If I was driving again for 12 seconds at a constant velocity/speed of 40m/s, how far did I go? Same thing, use the distance formula, d=vt, d=40(12), which is 480 meters. If I turned my car around and around, at a constant speed, I wouldn't be going at a constant velocity because I'm changing direction.

Constant Acceleration

Acceleration is the speeding up and/or slowing down of an object. Constant acceleration is calculated by the change in velocity over the time interval (^v/t=a [^=a triangle=change in]). Acceleration is in the units of meters per second squared (m/s^2). Just like velocity, we can use formulas to find how far and fast something was going/in a certain acceleration.

Here you can see this car acceleration at a constant acceleration of 2m/s^2. It started at a speed of 0, so every second it accelerated 2m, so by the time of 5 seconds it was going 10m/s. This is our speed/velocity formula we use: v=at. You plug in 2 for a and 5 for t, so 5 doubled is 10. We can also see how far it went after 5 seconds. The distance formula for constant acceleration is d=1/2at^2. If you plug in 2 for a and 5 for t again, solve it, you can see that the car went 25 meters.

Here are 3 ramps, the ramp on the left is a constant accelerating ramp because it slopes down perfectly to have a constant acceleration. The middle ramp has a decreasing acceleration because as a ball goes down the ramp, the ramp gets bigger, so therefore it has a decreasing acceleration. The last ramp is one that drops completely, making the acceleration increase.

Using a Graph (Equation of a Line) To Solve Physics Problems.

Here I learned that with certain graphs with equations of lines I can find the constant velocity, acceleration, and distance an object was going. 

If I was given an equation of y=4x, I can see this equation is close to the velocity equation of d=vt. On the graph, the y-axis is distance, and the x-axis is time, so I plug that into the equation of the line to get: d=4t. I can see that 4 is the constant velocity and I can plug in any time to find the distance.

Using the same equation for a constant acceleration graph, I can see that it's close to the distance formula for constant acceleration too. Plug the values in again; d=4t^2, but wait, where's the 1/2 you might ask. The acceleration is already halved, so to find the actual acceleration, you just double the number there, so in his case the acceleration would be 8m/s^2.

Here is more information/a video of how to do this in more depth:

All of this is what I learned from my first unit in Physics! I really like this class and hope to learn more new and cool subjects like these.

Hovercraft Questions

1. Riding ob the hovercraft was fun and what it did was make a loud noise, vibrate a little, and slide smoothly across the floor. I would tell anyone to try riding a hovercraft because it was cool and an experience that everyone should have done. Riding a skateboard and sled is different because it wouldn't keep in motion with all the friction under it.
2. I learned that the hovercraft kept going because of inertia, Newton's first law; an object in motion tends to stay in motion unless acted upon another force. The hovercraft was at equilibrium when it was moving at a constant velocity, with 0Newtons. Also when we were stopped (at rest).
3. Acceleration seems to depend on the amount of force being pushed or pulled, and this force helps the acceleration speed up/increase.
4. I was having/in constant velocity when I kept moving across the floor on the hovercraft in a straight line at the same amount of force from first push.
5. Some members were harder to push or move because of their weight. If they were heavier, it would take/we would have to make/do a bigger force to push and move them across the floor and hover.
6. Picture:

Inertia

In this video, one of the demonstrations was the guy pulled back the chair with a stack of books on it and pushed it against another chair. What happened was the moving chair hit the other chair causing the moving chair to stop and the books to keep going yet stay on top of each other, then they crashed into the wall to fully stop. That demonstration showed Newton's law of an object in motion tends to stay in motion unless stopped by a force. The object in motion was the chair with/and books, and the force that stopped the chair was the other chair, but the force that stopped the books was the wall, and they stayed on each other. 

Starting Physics

I have heard from friends and other who have taken Physics before that the class is a hard but fun class. They have said they have learned many things and some of the things I found interest in. Once they finished the class they also realized of how physics is all around us and how important it is. I wanted to take this class to find out how various things work and how they help us in our everyday lives.

What do I expect to learn in Physics this year?

One of the things I want to learn in Physics is how a microwave uses rays to heat/cook up food for us. I always thought it was heat from the light when I was younger but then was told it wasn't. I also would like to know how when we hit the brakes on the car, or get in a car accident our seat belts hold us in place and how the airbags know when and how to pop out to protect us. One last thing I would like to learn is how a rocket can move in outer space when it has no force to push off of.

Why do I think Physics is important?

I think Physics is important because we have it in our everyday lives. Once we learn the simplest things Physics is we can use it and expand on it too. Another reason is Physics shows us how everything works and if anything happens we can figure out/remember what to do when we are in trouble or just need to know how to fix something. It's also important in how we are. Physics is studying energy, and we humans are full of it. We can have positive energy or negative energy. When we have positive energy we attract more people and the opposite for having negative energy. Atoms, energy, and other particles/things around us all have their own energy and attract different things in their own way. This is what we need to learn how and why, and this is why Physics is important.

What is problem solving?

Problem solving is when you have a problem, then you take observations and clues that help solve it, and you work/calculate what needs to be solved. You need to identify the problem, figure out different ways of solving it, then keep trying to solve it until solved.

Questions I have for Physics

1. Who were some of the first physicists?

2. Why do certain items with different weight fall and hit the ground at the same time?

3. Where do we see Physics in our everyday lives and how does it work in those certain cases?

Goals I have for Physics

1. I want to figure out and learn where and how Physics is all around us in our everyday lives.

2. I want to succeed in the class yet learn and see Physics everywhere I go (learn in class and use it outside of class.)

3. I would also like to do various labs that are fun and cool to learn about Physics.