Galants10's Blog

Collision and Impulse models

galants10 — Sun, 21 Feb 2010 18:49:37 +0000

The way that the velocity of an object changes when it is subject to an impulse (very large, very brief) force.

–Impulse is (force)(time)

–Impulse = (mass)(change in velocity)

The relationship between the initial and final velocities of two objects that undergo a collision ( a very strong but very brief interaction).

–∆p1 = ∆p2 — they are inversely proportional- when two cars interact, one car’s momentum decreases as much as the other’s increases.

–(∆v1)(m1) = – (∆v2)(m2)

7.1-7.3

galants10 — Sun, 21 Feb 2010 18:48:08 +0000

In this section of the book we learn about momentum. Momentum is the inertia of motion and can be calculated by (mass)(velocity). This explains why a heavier object would have a faster momentum than a lighter object if they were moving at the same speed. The greater the force is, the more the object will accelerate which increases the velocity. If masses are the same, the object with a greater velocity will have a greater momentum. We learned that impulse is (force)(time) but can be calculated as (mass)(change in velocity). Impulse is also the change in momentum. Impact is the force that is used in the impulse equation. If the length of time of the impact is long, the force will be much lower than if the impact time was short. In our collision lab we found that if we graphed the impulse vs. change in velocity, that gave us the mass.

8.5-8.6

galants10 — Sun, 21 Feb 2010 18:47:47 +0000

Kinetic energy is the energy of motion. The formula for kinetic energy = ½ mv^2. The text explains how work is related to the increase and decrease of speed. Work can also be described as the change in energy. Therefore, Work = (force)(distance) = ½ mv^2. We also read about an idea that we previously talked about in class; the idea that energy cannot be created or destroyed, and that it simply is transferred. This is the law of conservation of energy. This is a very important concept in physics because as we study different topics, we will be able to use this law to help us find information. If we know a totally amount of energy and how much of it is in one form, we can figure out how much is in the other forms of energy.

Car on Ramp Lab

galants10 — Sun, 21 Feb 2010 18:47:27 +0000

This lab is divided into two parts. As discussed in the previous blog entry, we set up a ramp with a car at the bottom. In the first lab, the car was propelled up the ramp by the spring’s energy, and the second lab we manually pulled the car up the ramp with the force scale. In both labs, the same work was being done, just by different things. The spring was doing the work in the first lab and we were doing the work in the second. This lab allowed us to see how energy can be transferred from one form to another. We also saw the relationship between force, angle, and distance.

8.1-8.4

galants10 — Sun, 21 Feb 2010 18:46:55 +0000

Work = (force)(distance). When force is applied to an object, and that object moves a certain distance and those two measurements multiplied by each other is force. Work is measured in Joules. This chapter also talks about power. Power= work done divided by time. it is measured in watts which is joules per second. In class we did two labs to measure work. We set up the car on ramp lab and for one experiment we pushed the button, which activated a spring, launching the car up the ramp. For the other experiment we manually pulled the car up the ramp using a force scale. In the first lab we were able to find the spring constant by graphing the relationship between force and the change in length. We got a linear graph so the slope was our spring constant. Mechanical energy is also discussed in this chapter. It is the energy due to position or motion of an object. Mechanical energy can be either potential energy, the energy stored in an object, or kinetic energy, energy of motion. Gravitational energy is the amount of energy needed to pull an object against earth’s gravitational pull.

Reflection of Unit One

galants10 — Tue, 12 Jan 2010 15:51:40 +0000

1. What do you know now that you didn’t know before and how did you come to know it?

I didn’t know the effects of having spin on the ball in a projectile. My group’s project was to analyze whether a float (no spin) and a topspin volleyball serve would have the same velocity. We found that the topspin speeds up and the float has more air drag so it doesn’t speed up like the top spin does.

2. What do you know DIFFERENTLY than you “knew” before and how did you come to CHANGE what you knew?

I thought that both horizontal and vertical velocity affected air hang time but we have learned from our projectile motion labs that the horizontal velocity does not have an effect. When jumping in the air, if there is equal vertical velocity, one will spend the same amount of time in the air if they jump straight up as if they jump forward a few feet.

3. Looking back over the past unit, how did you approach your studies and your quest for UNDERSTANDING?

When learning physics it is important to have an open mind because we have an idea of how many things work in our world but exactly why or specifically how it works. We must also be ok with having ambiguous answers while trying to figure things out until we can put all the pieces together to have a clear definition or reason for why something happens the way it does.

4. As you move into the next unit, what can YOU do to improve your results towards UNDERSTANDING? What changes can you make to your approach to learning?

I need to ask more questions and continue to question our methods until I fully understand what we are talking about. Our board meetings are good times to bounce ideas off of each other so I need to utilize that time better to solidify my understanding of whatever topic we are covering.

11.4-11.7

galants10 — Tue, 12 Jan 2010 15:19:08 +0000

Inertia is the resistance of an object to change its rotational motion, so an object at rest stays at rest, and an object in motion will continue to be in motion. Torque is what is required to change the rotational state of the motion of an object. The greater the distance between the bulk of the mass of an object and the axis around which the rotation occurs, the greater the rotational inertia will be. The formula for calculating it is I=mr^2. Rotational Inertia creates angular momentum while mass and velocity create linear momentum. The formula for angular momentum = rotational inertia x rotational velocity. Rotational inertia and rotational velocity are inversely proportional, as one goes up the other goes down.

9.1-9.3

galants10 — Tue, 12 Jan 2010 15:05:42 +0000

An axis is a straight line around which rotation takes place. When the object turns about an internal axis, it is called a rotation. When the object turns about an external axis however, it is called a revolution. When discussing speed you must consider two types: rotational and linear. Linear speed is the distance moved per unit of time. The outside of a circle has to move a greater distance in the same amount of time as the center, so it is moving at a greater speed. This is also called tangential speed. Rotational speed is the number of rotations per unit of time. in this unit, the people on the outside and the people in the center have the same speed because they have the same rate of rotation. A force that follows a circular path is called a centripetal force.

In class we watched videos of ice skating and divers doing spins and we analyzed the speed at which they rotated. When they were tucked in, creating a smaller radius, they sped up, and when they were taking up a larger space they slower down. When the radius is cut in half, the speed doubles and the rotation rate quadruples.

Air Resistance

galants10 — Tue, 12 Jan 2010 15:05:07 +0000

In class we talked about the effect of air resistance on the motion of a projectile. The horizontal motion, if graphed on a position vs. time graph, would be curved because it would slow down due to the air drag. The vertical motion on the same graph will be steeper in the beginning and slowly flatten out. In velocity vs. time graphs the horizontal motion will get close to zero but there is an asymptote so it does not quite reach zero. The vertical velocity starts at positive and has a negative slope. When the vertical velocity is at zero, that is when the object is at its peak and there is no air resistance.

3.4-3.5

galants10 — Mon, 23 Nov 2009 06:03:38 +0000

In 3.4 it talks about projectile motion. Looking at the horizontal and vertical components separately can simplify the path that the object takes. When no horizontal force acts on the projectile, the horizontal velocity remains constant. On the other hand, the vertical direction has the force of gravity. This causes there to be an increase in speed. The horizontal and vertical components are completely independent of each other. In 3.5 we learn that if air resistance is negligible, a projectile will rise to its maximum height in the same time it takes to fall from that height to the ground. Because gravity is constant the deceleration going up is the same as the acceleration going down.

Question 9- The force of gravity acts on both of them but the downward projectile is slightly curved while going down.

Question 12- It will reach the maximum vertical altitude if shot at 75 degrees and will reach maximum horizontal range at 45 degrees.

Question 35- One would think that both the vertical and horizontal components affect hang time but in fact only the vertical component affects it. Once you jump in the air the only force being activated is gravity so the velocity of the vertical component is what determines hang time.

Question 36- Because the horizontal component does not affect hang time, it will be the same 2/3 second.