Unit 3

In this unit I learned about…

            -Newton’s Third Law (Every action has an equal and opposite reaction) along with action reaction pairs.

            -How people win tug of wars in relation to physics and why a horse is able to pull a buggy (both problems that are in correlation to Newton’s Third Law).

            -Forces in perpendicular directions

            -Gravity and Tides

            -Momentum and Impulse Momentum

Newton’s Third Law

Newton’s Third Law states that every action has an equal and opposite reaction. For example: truck hits car/ car hits truck. This is an example of an action reaction pair. Action reaction pairs are two equal and opposite forces of which include equal sizes and opposite directions.

Here are some important example problems:

            How does a horse pull a buggy? Label the action reaction pairs, and explain your reasoning.

In this diagram we can pull out three action reaction pairs. These are commonly shown through vectors. It is important to note that the strength of the pull does not matter. The horse will pull the buggy with the same force the buggy pulls the horse with. We know this from Newton’s Third Law that states, “every action has an equal and opposite reaction”. The reason the horse is able to pull the buggy is because the horse is pushing the ground harder than the buggy does. The horse and buggy will move in the direction of the horse.

  The first pair is between the two opposing forces.

The top vector will be labeled “Horse pulls buggy”.

Where as, the bottom one will note, “Buggy pulls horse”.

The second one is that the “buggy pushes ground” and “Ground pushes buggy”. The third being “horse pushes  

ground” and “ground pushes horse”. Make sure the horse’s vectors are longer because it shows that the horse is pushing the ground harder than the buggy.

Forces in different Directions

When we add vectors there are two special coincidences. If one is when the vertical and horizontal are the same number, the diagonal is 1.41. The other is when 5, 4, and 3 all go together. This way we can see easily how to figure out what direction the object will take.

For example: If a 100m/s canoe is paddling down a river with a 100m/s current, what path will the canoe take?

            It will go in between the two at 14.1 m/s.

Gravity and Tides

            If you look out at the ocean you will notice when the waves are closer, and when they are further. These are tides. There are high tides (when it comes further up on the beach) and low tides (when its lower on the beach).

These switch back and forth. There are two high tides and two low tides every 24 hours. It takes about 6 hours for tides to switch from high to low, meaning it takes 12 hours to go from low tide to low tide or from high tide to high tide. The reason for tides is the difference in force felt by opposite sides of the earth. This is just another example of an equal and opposite force, as the moon pulls the earth while the earth pulls the moon.

Sydney Sloan did the diagram above.

This shows the moon’s affect on the earth’s tides. Side B has a greater distance and a smaller force, while side A is the opposite.  The distance has a great affect on the force.

The Universal Gravitational Law is F=Gm1m2/d². This problem essentially demonstrates the relationship between force and distance².

The dotted line around the earth is known as a tidal bulge. The tidal bulge is created by the difference in between the forces between A and B.

For example:

If side B had a force of 2N and side A had 6N, the middle force would be 4N. If we solve for B, we would subtract 6 from 4 and get -2N. And side A would be 6-4 and be 2N.

There are two types of tides: a Neap Tide and a Spring Tide. This has to do with the positioning of the sun, the moon, and the earth. A spring tide is when all three align, proving higher tides. This normally occurs during a full moon. A neap tide is when the moon is perpendicular to the sun in relation to the moon.

Momentum and Impulse Momentum

Momentum (p) is the product of an object’s mass and velocity. Furthermore, p=mv.

The change in momentum is formatted as ∆p=pfinal-pinitial.

We also know that Impulse (Ft) is the force multiplied by the time it is applied. In other words, J=F∆t. Along with this, Ft is equivalent to ∆p.

For example:

1.) What is the momentum of a 10kg carton that slides with a 3m/s?

p=mv                          p=(10)(3)                  p=30kgm/s

2.) In Frozen, why did Anna and Sven not get hurt when they fell off the mountain and landed in snow after being chased by the snow monster?

                                    p=mv                          ∆p=pfinal-pinitial

Anna will go from moving to not moving regardless of the surface she hits. This means that the change in p will stay the same regardless of the surface. If this is so, we know that J will remain the same as well because J=∆p. Another important aspect in answering this problem is that J=F∆t. Because snow increased the time of Anna’s force it decreased the force. Less force simply means less injury.

J=F∆t  and  J=F∆p

3.) Why don’t cars have rubber bumpers anymore?

            The cars will bounce causing two changes in p’s and two J’s. Furthermore, there would be double the force and more injury.

Tides Resource

Unfortunately, many people believe that tides are caused solely by the moon. However, the moon, the sun, and the Earth's rotation are all contributing factors to the pull of tides. The Earth rotates between a time span of 24 hours. Within this time, there are 2 high tides and 2 low tides. This means that every 6 hours the tide will shift from high to low or vise-versa. Noticeably, the moon is closer to different sides of the earth at different times, this is due to rotation. The side closest to the moon experiences the greatest force while the side farthest from the moon experiences less force. This video explains this by using a metaphor of a hose and objects. The object closest to the spraying hose experiences greater water pressure. We know this because of the formula: F=Gm1m2/d^2. Force is both affected by distance and mass. The radius of the earth greatly alters the distance. We also know that force is directly proportional to mass and inversly proportional to distance. In this way the side farthest from the moon experiences the smallest force. This difference in force creates a tidal bulge.  This happens because compared to the middle, there is a net force in opposite directions, on either side of the earth. During a spring tide, the sun, the moon, and the earth aline. This creates higher high tides and lower low tides. When they aren't in a line, it is a neap tide (normally the shape of an L). This video does a great job of further explaining this concept.

In this graph, we can see that Nags Head is currently in between high and low tide. Because it is a full moon, we are in a spring tide.

Newton's Third Law

This video helped explain Newton's Third Law by providing examples in Football. The physicist narrates two football players in mid-tackle. Right away, we can observe that the one with more mass was able to take down the one with much less mass. I struggled with this concept in class initially. The video emphasizes that although he might be stronger, the push and force have no influence on the outcome. Overall, the video helped me to understand this tricky concept. For more information on Newton's Third Law, watch the video!

In order to further our understanding of Inertia along with Newton’s first law, we experimented with hovercrafts. I must say after having ridden the hovercraft, that it is probably one of the strangest experiences I’ve had in a science class. For starts, its nothing like being in a car or a bike. There is no control of direction, nor is there any brakes. If you aren’t familiar to hovercrafts, it feels as though you are floating. That being said, being on a hovercraft feels incredibly weird and awkward. That is, until you realize what is happening. According to Newton’s first law, an object in motion will continue to stay in motion until stopped or slowed by an outside force. Once my classmates had pushed me, the hovercraft was unable to stop until the other students stopped me. The people both starting and stopping contributed to something called a net force. The net force is the addition of all the forces that are acting upon an object. When the total is zero, it means the forces have reached equilibrium, meaning both forces are balanced. An outside force that gives it speed determines acceleration. For example, when my classmates pushed me, the hovercraft accelerated. After it had reached a consistent speed, it had a relatively constant velocity. Some of the members of my class were harder to stop than others. This was due to they’re mass and weight. The tiny kids went really fast, but as size increased, the speed decreased. This was simply because of the pressure of the person on top of the hovercraft. Overall, it was really fun.

Inertia

As usual, Bill Nye is able to explain complex terms into something a little simpler. In this video, he does so by explaining inertia by using two scooters. The two scooters demonstrate Newton's first law, which states, "An object in motion, or an object at rest will remain in motion unless acted upon by an outside force". Simply put, it is the idea that an object will continue to do what they are doing, until something causes it to stop. This "something" could be the roughness of the ground, an object in its path, etc. Bill Nye helped me to come to a deeper understanding of this concept through his demonstration. Bill Nye, said it himself, the two scooters are forcing the other to change directions. However, Nye makes it clear that without another force, the scooter would continue to move. Normally, we tend to forget the significance of small forces. In this particular video, we see the influence of which something simple as a chain has a huge impact on the movement. The ball would continue if not for the tension in the chain. This video made it understood that small forces, ones we subconsciously look over, have an affect as well.

Physics Blog

In physics this year we will most likely learn:

1.     Speed

2.     How things move, and project others to move.

3.     Tides

I think it is important for us to study physics to gain a deeper understanding of what is happening around us. A lot of times, we don’t notice how something small that seems to have little value, has a huge impact on what happens in our daily lives. With physics, we have the opportunity to recognize these impacts, and their significance.

            Problem Solving is looking for the most efficient way to a solution of something that has gone wrong.

1.     How does the moon, which is so far away, have control of the tides?

2.     How does an object of heavier weight drop at the same rate of a smaller object?

3.     When am I going to use the content studied in the class?

Through out the year, I will strive to answer these questions to the best of my abilities, gain a deeper understanding of physics, and maintain a high effort grade.