Unit 3.

Newton's 3rd Law says whenever an abject exerts a force on a 2nd object, the 2nd object exerts an equal and opposite force on the first.

For example, Gravity pulls book downward. Book pulls gravity upward. Notice the underlined words: with an equal and opposite relationship, there must be the same verb, opposite directions, and the same two objects.

If the relationship was: hand pushes apple up, gravity pushes apple down, apple pushes hand down. This would only be an action and reaction pair because of the 3 different objects that are used. 

For an object to exert an equal and opposite force there must be only 2 objects exerting the force; just think of it as equal and opposite, one object and two object. 

In this example, the horse and the buggy and the equal and opposite pair. However, with the ground, horse, and buggy this is an action and reaction example. As the horse pulls the buggy forward, the buggy pulls the horse backward with an equal and opposite force. What makes the horse go forward is the horse's friction on the ground. Because the buggy is on wheels it does not have friction. Thus, because the horse's force on the ground is greater than the buggy's force on the ground the horse will move forward.

When drawing this picture, you need to make sure of to very important things: (1) that the vector at the top is equal and opposite (2) that your arrows point in the direction the word says (backward = back arrow).

Also, in class we did tug of war with girls vs. guys, and surprisingly the girls won!!! How did they win? Well, we made the boys place really fluffy, slippery socks on their feet, then went to the slippery floor. While the boys had socks on, the girls had their feet on the ground. This is similar to the horse and buggy demonstration. The girls had more friction on the ground, thus they were able to pull the boys and have more force, since the guys had on socks and didn't have a support force with the ground (friction). Because of this, the girls won the tug of war!!

This video is an example of vectors and adding forces. It demonstrates how to make vectors and when you might use them.


The next subject we learned in this unit was gravity and tides. One of the most important things to know is that tides are not caused by the force difference between the moon and earth or sun and earth. Tides are caused by the difference felt on opposite sides of the earth.

Everything with mass attracts all other things with mass.

Because the sun has a larger mass, it has a greater force on the earth than the moon does. It's important to remember that force depends on two things: (1) mass of object (2) distance between objects

       Thus, the inverse square law 1/d^2.

And the Gravitational Force Formula is F = G (m1m2 / d^2) N  =  which is how someones weight is calculated.

This explains why a persons weight decreases as they get farther away from the earth (ground), for example, on Mt. Everest a person's weight is lower than when they are standing on the beach. 

The two different tides are spring tides and neap tides. Spring tides are when the lowest are at their lowest and the highs are at their highest (then normal). Neap tides are when the highs are at their lowest and the lows are at their highest. 

The change in P (momentum) is the same regardless of how you are stopped. 

P = mv

(change in) P = Pfinal - Pinitial

Impulse is the force upon something and how long force is applied -- force x time = force applied. 

Impulse = Force x change in time

J = F x (change in) t

Thus Impulse and (change in) Momentum are equal. J = (change in) P.

So why do airbags keep us safe??

The car wil be going from moving to not moving ( P = mv) & (change in P = Pfinal - Pinitial)

         Thus the P is the same

The impulse will be the same regardless of how you are stopped ( J = change in P) 

         Thus impulse is the same (J = F change in t)

An air bag increases the time of the impulse, thus the force is smaller. 

When a car goes from moving to not moving there is a conservation of momentum. Say a car that weighs 2kg is going to the right at 3m/s and the second car that weighs 3kg is going to the left at 3m/s. After the collision, the cars are stuck together. What's the final momentum? 

This is how you find it.

Unit 2 Review : Test

This lab was centered on Newton’s Second Law, which is acceleration is directly proportional to force (aka as force increases then acceleration increases, as force decreases then acceleration decreases). Also, acceleration is inversely proportional to mass (aka as mass increases then acceleration decreases, as mass decreases then acceleration increases).

If an object has less mass it is easier to accelerate.

 When an object is going downwards or is being pushed downwards, weight = mass x gravity and gravity is similar to acceleration as in that it’s 10 m/s^2.

In the Newton’s 2^nd Law lab, we had a cart that was accelerating with a hanging weight that was the force of the system – as learned in Newton’s 2^nd Law, acceleration is directly proportional to force. Say if the hanging weight is 3kg and the cart is 2kg. The total mass of the system would be the cart and the hanging weight added together (and anything else added on), which would be 5kg. Use the w=mg to find the net force (Fnet) of the system. Since the hanging weight is the force, you plug in 3 for mass and gravity is 10, so the equation is w=(3)(10); this equals 30 N.
When Skydiving, as speed increases the force of air resistance increases (FAir); thus, speed is directly proportional to air resistance.

F-weight causes you to accelerate, since you’re accelerating you speed up. Every second you continue to go down, your F-weight will always stay the same. To find the Fnet of the skydiver, it is F-weight – FAir = Fnet. The two things that affect Air Resistance is speed surface area (both directly proportional to air resistance). When a diver’s air resistance increases to the amount of the Fweight (they are the same value), then using the equation (since they’re the same amount) the Fnet will be 0m/s^2. In the 1^st unit, Newton’s 1^st law, we learned that when the net force, or acceleration, is 0m/s^2 then the object is at equilibrium, which means the person is at terminal velocity. Another time an object can be at terminal velocity is when it is moving at a constant velocity. This terminal velocity is very fast. When the parachute is opened, the air resistance increases, and since you subtract the air resistance from the weight, the net force becomes negative (aka the acceleration is negative). We learned in the first unit with the hovercraft that when the net force, or acceleration, is negative the object is slowing down. Which is why using a parachute is safe because it slows someone down. However, as they slow down the air resistance beings to decrease, and at that point their air resistance beings to equal their Fweight (terminal velocity); however, now it is at a much slower equilibrium. 
Skydiving and free fall are two different things, but it's easy to confuse the two.
In free fall, the only thing acting upon an object is gravity only. The force due to gravity on a mass is the same as its weight >> w=mg. In the first unit, with constant acceleration, we were able to find how far and how fast an object went with two formulas

Say someone is about to go cliff jumping, and they will hit the water in 3 seconds. You can figure out the height of the cliff by using the "how far" formula >> d= .5 (10)(3^2) >> d= (5)(9) >> d=45m. And with that information you can figure out "how fast" the object was moving >> v=(10)(3) >> v=30m/s. 

If an object is thrown straight up, it will only have a vertical velocity and not a horizontal velocity. If given the time or the velocity, you can figure out the other one needed and also the height. At the top of its path, the object will have a velocity of 0m/s (aka it is not moving). However, you always have to make sure that when the ball is at rest (when you first throw it), the time will always be 0s, or else your data will be completely wrong. 

If an object is throw up at an angle, the only thing that determines the time in the air is the vertical velocity. At the top of its path, the object will still be moving, unlike the object thrown straight up. This is because an object thrown at an angle will always have the same horizontal velocity all throughout its time in the air. With this, there are two special right triangles we will use in class. 

Cause I'm Free Fallin'

In this video, there are people jumping from this very high cliff - they are in free fall. When an object (or a person) is in free fall, the object (or person) falls due to the effect of gravity only. Gravity is equal to acceleration, which would be 9.8 m/s^2. You know this because the force due to gravity on a mass is the same as the weight. We know two different equations for this. A = Fnet / Mass and also
W = M x G. Since force is the same as weight, you can plug in what weight equals for Force (Fnet), which would equal A = M x G / M, and in this equation the mass on top and the mass on bottom cancel out which result in A = G.

As the diver's Fair (the speed or the surface area are both proportional to Fair) continues to increase to the point that the Fair is equal to the Fweight, the diver will then be at equilibrium, or terminal velocity.
The diver opens the parachute so that he will be able to reach the ground with a safe speed, instead of hitting it with a *splat!* The parachute is used to help the diver's speed decrease so that when the parachute opens, the diver will be able to fall freely towards the ground. 

Newton's 2nd Law

In this video, the students are demonstrating Newton's 2nd Law, which states that acceleration is directly proportional to force and acceleration is inversely proportional to mass. The larger marble is rolling down the ruler and hitting the smaller marble. Because the larger marble has more mass, it creates a greater force on the smaller marble. A greater force means that the marbles will have a greater acceleration (since acceleration is directly proportional to force). However, when the smaller marble is rolling down the ramp, it creates a smaller force. Since the smaller marble as a smaller mass, the force it hits the larger marble with will be decreasingly different from the force the large marble hit the small marble. Thus the acceleration will be slower when the smaller marble hits the larger marble. The difference between the two marble's acceleration is because of their difference in mass which creates a difference in their forces.

Unit 1 Review: Test

In this unit, the major concepts were: Newton's 1st Law, Inertia, Net Force and Equilibrium, Acceleration, Velocity, and how to tell Acceleration and Velocity apart using different equations for each.

Newton's 1st Law is that an object in motion will stay in motion unless acted upon by an outside force and an object at rest will stay at rest unless acted upon by an outside force. For example, table settings are on the table with the tablecloth underneath. The settings on the table are at rest. When the tablecloth is removed from under the settings, the settings will stay at rest because of Newton's 1st Law, which states that an object rest will stay at rest unless acted upon by an outside force. 

As shown on the video, the girl removes the tablecloth and the settings (the bowl) stays in place because of Newton's 1st Law.
We can see Newton's 1st Law in everyday life when we accidentally leave our coffee cups on the top of our cars. The coffee cup is at rest on top of the car. When the car accelerates forward, the car is removed from under the cup (just life the tablecloth example). The cup falls exactly underneath was it was on the car because of Newton's 1st Law, which says an object at rest will stay at rest unless acted upon by an outside force.

Inertia goes along with Newton's Law because it's basically saying that objects like to keep on doing what they're already doing, unless a force is acted upon to make it change. For example, when on the hovercraft we needed a force to move us from our position at rest (at the beginning) and a force to stop us from moving (at the end). During this experiment, we learned that the more mass you have that more inertia you have. Because when trying to stop the hovercraft, it was harder to stop for those that had more mass, but it was easier for those who had less, which means that your mass depends on your inertia.

While on the hovercraft, we had a feel for what equilibrium was. When we were at rest, we were at equilibrium and when we were moving at a constant speed we were also at equilibrium. An object is at equilibrium when it is either at constant velocity (no speed or the same rate) or when the object is at rest. Something that's important to know about an object being at equilibrium is that when at equilibrium the net force will be 0N. Net Force is the force pushing against an object or the force at which it is at rest. When at object is at constant velocity, the force of friction (going on direction) will be equal to the amount pushing the opposite direction.

In this picture, there are 50N pushing to the left and 50 N pushing to the right. Because there are an equal amount on each side the net force is 0N and the object is at equilibrium. 

Acceleration is the change in velocity over a period of time. You can change your velocity in 3 different ways: speeding up, slowing down, and changing direction. If there is no change in velocity, there is no acceleration. I always forget that change in velocity is change your direction, so easy way to remember is that they are both "changing."Acceleration happens in everyday life when you're changing your speed in a car or when you're walking. Acceleration is measured is m/s^2. If an object is at constant acceleration, there are two different formulas used for measuring how fast and how far the object is going. How fast is velocity equals acceleration x time. How far is distance equals 1/2 acceleration x time ^2.

If a ball is rolling on a flat surface:

Then the velocity is constant and there is no acceleration, 0 m/s^2

If a ball is rolling down an inclined ramp:

Then the velocity and the acceleration are increasing.

If a ball is rolling down a curved ramp:

Then the velocity is increasing, but the acceleration is decreasing.

If an object is free falling, then it is going at 10 m/s^2

If a car is traveling at a constant speed, then it is traveling with a constant velocity. When at constant velocity, then the acceleration is 0 m/s ^2. The equation for constant velocity is velocity = distance / time. Even if an equation asks for how fast or how fast a car, or an object, is going, if it is going at a constant speed, then it is automatically going at a constant velocity. 

If something has constant velocity then it cannot have constant acceleration because with constant velocity you're covering the same amount of distance with the same amount of time. But with constant acceleration you're speeding up.

When studying this section, I found figuring out when an object has velocity and when it has acceleration difficult. However, the diagrams (shown above) made it easier to understand. 

Constant Velocity Vs. Constant Acceleration

This lab was to test the difference between constant velocity and constant acceleration. It gave us an idea of what the two were and what the difference between the two is; it helped further explain the definition because it showed it what it was not just being told what it was. Constant velocity is when an object (in this case the ball) covers the same distance in the same amount of time ( 0.5 seconds ), and the formula used for it is V= distance / time. Constant acceleration is when an object (the ball) is speeding up and covering more distance per time, and there are two different formulas used for it: how fast somethings going is V= a x t and how far somethings going is D= 1/2 a x t(squared). In the lab, we first tested constant velocity by rolling the ball on flat surface and marking every 0.5 second where it was. Then after we got our data, we put it into Microsoft Excel and found out our equation. Similar thing for constant acceleration, but instead we placed two books under one side of the table, so that the table was inclined, and rolled the ball down. For this, the ball had constant acceleration because the inclination was the same going down. Both lines, for constant velocity and constant acceleration, are increasing to the right. For constant velocity, my graph and data show that as time increases the distance also increases at a constant rate. For constant acceleration, the graph and data show the same thing, however, the distance does not increase at a constant rate. From this lab, I learned that when I am absent I day that I must email Ms. Lawrence and ask her what I missed. Also, I learned that it is important to pay attention to what is going on and make sure that you understand what to do, and if not make sure to ask peers questions and Ms. Lawrence questions. The third important thing I learned is the difference between the two constant acceleration formulas; the difference hadn't hit me until I actually looked at it and acknowledged that how far would be distance because far is going somewhere, while how fast is velocity because your covering the distance; knowing this made me really happy.

Hovercraft: Gliding on Air

a)
 Riding on a hovercraft feels like you're gliding on air. As you observe other classmates (or someone else) riding the hovercraft, you believe that the hovercraft is going very slow. However, you're observation is wrong as soon as you get on it and you begin to glide. One of the most important keys to riding the hovercraft is making sure your weight is evenly distributed throughout the hovercraft so that the hovercraft can be balanced through the air and have a smooth glide.

Riding a sled, skateboard, etc. is different than riding a hovercraft because on such transportations there is friction on the bottom of the objects, which because of friction the objects will eventually come to a stop. This is because of Newton's First Law, which says that an object in motion tends to stay in motion unless acted upon by an outside force. In this case, the friction is the outside force.

b)
Inertia: The more mass you have the more force you need to stop the hovercraft.
Net Force: As the hovercraft is moving forward there's a certain number of Newtons acting upon it that keep it continuously moving forward. However, when Walker becomes the outside force causing the hovercraft to come to a stop, his number of Newtons is higher than the hovercrafts, which is why the hovercraft stops.
Equilibrium: As you're on the hovercraft in the air, you can feel the how it's balanced; that it is actually gliding through the air.

c)
Acceleration depends on an outside force pushing the hovercraft to increase it's speed

d)
I would expect to have constant velocity as I'm gliding through the air on the hovercraft. For example if I'm on a skateboard I'd expect to have constant velocity as I'm gliding through

e)
The members of the group that were harder to stop were the ones that had the most mass.