Momentum!!

Our new unit that we are concentrating on focuses on...

Momentum!

Momentum is abbreviated with the letter P (I know, m was already taken). Momentum is the quantity of motion of a moving body, measured as a product of its mass and velocity.The law of conservation of matter states that in a isolated system, momentum will be conserved. Impulse is the change in momentum. We also learned a couple of equations...

Momentum(in) = Momentum(out)

Momentum = mass(kg) x velocity(m/s)

(Therefore, momentum's units are kg(m/s))

Impulse = P(final) - P(initial)

(Therefore, impulse is the change in momentum)

Impulse = F (average force) x t (time)

One of the most important concepts that we learned about had to deal with the last equation: Impulse = (avg force)(time). This equation explains the relationship between impulse, force, and time. When impulse increases, force and time also increase (direct relationship). Force and time have an indirect relationship that means that as force increases, time decreases and vice versa.

My clumsy sister always drops her phone! She drops it outside, inside, off the table and anywhere imaginable. Today, she dropped her phone twice: once on the carpet in my living room, and once on the tile floor in the kitchen. When she dropped it on the carpet, it was fine and she picked it up. But when she dropped it on the tile floor, it cracked open and fell apart. This is a great example of the relationship of force and time! (But not so great for her phone) Remember: impulses are the same because the change in momentum are relatively the same. When the phone dropped on the hard tile floor, the time the phone had to reach velocity zero was very small, making the force a lot bigger. In comparison, the phone that dropped on the carpet had cushion, which helped the phone not to break due to the increase in contact time. An increase in contact time helps to deplete force!

Therefore, drop your phone on surfaces that allow for more contact time!!

Forces that accelerate!!

Forces are fun!! When an outside, unbalanced force acts upon an object, the object accelerates. (When balanced forces act upon an object like rubbing your temples, the force stays at rest.) The inertia of an object causes it to continue until it is acted upon by another force.

This week we focused on forces that accelerate, which relates to Newton's second law: the acceleration of an object is directly proportional to the net force on an object; the acceleration of an object is inversely proportional to the objects mass. This means that when the force increases, the object's will acceleration will increase. As the mass increases, the acceleration will decrease, and as the mass decreases, acceleration is greater.

Let's take a look at an example!! After eating a tasty lunch with my sister, I got thirsty so she rolled me one of the drinks she bought. Knowing acceleration and the mass of the can we can find the force that my sister used to get it to me.

To find this, we would first make a free body diagram and then solve it using the only formula we know.... Fnet=ma!!

Yay forces!

Newton's First Law and Inertia!!

Unit 4 is all about forces! To understand forces better, we learned about the foundation of forces in motion: Newton's three laws. These laws were created by Sir Isaac Newton, a physicist born on January 4, 1643 in Woolsthorpe, England. His ideas became the basis of forces!

Let's focus in on the first of his laws, otherwise known as the Law of Inertia. Newton's Law of Inertia states that "objects in motion will tend to stay in motion unless acted upon by an outside, unbalanced force." This law could also be flipped by saying that "objects at rest will tend to stay at rest unless acted upon by an outside, unbalanced force. You might say, "What does that have to do with that thingy... inertia?" Well, in class we learned that inertia is defined as an object's capability to continue in the state it is in. We also learned that an object's inertia is directly proportional to an object's mass.

Okay, so what does this all mean? The typical thing for objects to do is to stay in the state that they were previously in. If no outside, unbalanced force interrupts this object, it will most likely stay in the state it was in.

Here is an example! (Sorry, it would be much better if I could upload videos but it doesn't let me. :( )

As the water bottle was being acted upon by an outside, unbalanced force (me pushing it), it broke its state of rest and began rolling (state of motion). When it hit the wall, it went from a state of motion to a state of rest. Why? Same thing! The wall is another outside, unbalanced force that changed the water bottle's state of motion to a state of rest. If the wall wasn't there, the water bottle would have kept on rolling along.

Newton's First Law helps us understand more about forces and how they work!!

More on Projectile Motion!!

While studying in Coffee Bean & Tea Leaf this fine Sunday afternoon, I noticed some physics going on! I payed for my drink and cornbread muffin and then went to sit down to study. When I put my wallet down, a quarter fell out of the pocket and fell to the ground. This reminded me of projectile motion!!





Now remember, there is one important rule to follow while using axes: the Vegas rule. In a previous blog post, I explained that the Vegas rule states that "what ever happens on the x axis, stays on the x axis" and "what ever happens on the y axis stays on the y axis". The only thing that is constant when trying to find either position, time, or range is that time is constant in both axes. If time is 3 seconds in the x, time is 3 seconds in the y.



My quarter is a wonderful example of projectile motion. The table that my quarter fell from was 2m from the ground. It fell at an initial velocity of 1m/s. We need to find where it's going to land to pick it up. Lets list our givens!!

With this information, we can use "dat" equation to find time (using info from the y axis)

d = 1/2at^2 + Vot

2m = 1/2(9.8m/s^2)t^2

2m = 4.9 m/s^2 (t^2)

0.408 = t^2

t = 0.64s

Fill in our givens table!

With this new info, we can find the distance it goes in the x axis!!

Use "dat" equation again!

d = 1/2at^2 + Vot

d = (1 m/s)(0.64s)

d = 0.64 m

If I wanted to catch my quarter off of the table, I would put my hands at 0.64 m away from the edge of the table. Great job!! Projectile motion is fun!