Ryan's Physics Blog

7.4-7.6

smithr1313 — Sun, 21 Feb 2010 23:32:23 +0000

The text begins by explaining that an impulse from an external force must be exerted on an object in order to change its momentum because without an outside force there wont be any momentum. Without an outside impulse acting on an object, the momentum of the object will remain the same. When there is no momentum change , it is called “conserved momentum.” The law of conservation of momentum states that the total momentum of an object does not change, momentum after collision is equal to momentum before collision. We observed many of these characteristic in our lab we did as a class. One thing we discovered in our lab was that when the masses are changed, we would get different data. The text ends by explaining how momentum vectors can prove the conservation of momentum by observing momentum from any direction as vectors.

22. a. The speed will be 3 m/s because the objects have the same mass.

b. The speed will be 1.5 m/s because the momentum must be equal before and after the collision.

27. a. The spring exerts a greater impulse. We know this because a greater impulse is required to stop an object than to push one.

b. Since the pillow only used a force to stop the ball and the spring used a force to stop the motion of the ball and push the ball, the force of the spring is greater.

7.1-7.3

smithr1313 — Tue, 02 Feb 2010 13:26:57 +0000

The formula for momentum is momentum = mass x velocity. Based on the formula mass x velocity, you know that an object with a larger mass will have a higher momentum than an object with a smaller mass when they are going the same speed. If the masses were the same, and the car with a smaller mass had a greater speed, it would have more momentum. Force also is a large factor with momentum. Force increases an objects momentum just as it increases an objects acceleration and the longer the force is applied, the more momentum it will have. An impulse is a change in momentum. An impulse occurs during a force x time interval. Force x time = change in momentum (mxv) which goes with what we found in our lab. An impact is a force that is used in the impulse equation. The longer an impact occurs, the longer the time the force is zero. More force applied means a shorter impact time. This reading introduced us to momentum and impuleses and explain what happens to objects during collisions and the text matches up well with what we found in class with our lab experiment.

8.5-8.6

smithr1313 — Wed, 27 Jan 2010 02:10:50 +0000

The formula for kinetic energy is Kinetic Energy = 1/2 x mv^2. We developed this formula from a lab and class discussion but the text introduces a new idea. How work relates to the increasing or decreasing speed of an object. The formula is Fd=1/2 mv^2. The Work-Energy Theorem says Work = Change in Energy. This implies that work determines the amount of kinetic energy. The text also introduces an idea that we have discuessed in class. The idea that energy transforms. Energy cannot be created or destroyed. Energy dissipates into new forms of energy constantly. This is known as the Law of the Conservation of Energy.

Pull up car lab

smithr1313 — Tue, 26 Jan 2010 13:37:50 +0000

One of the main points I took away from these two labs was that all moving objects have energy. From our two different labs involving the car on the ramp, we were able to determine that the energy required to get the car to a specific height is the same wether launching the car or pulling the car up the ramp by hand. The difference between the two labs was that in the firs tlab, by launching the car all of the energy was released at once. In the second lab, we were relasing the energy over a spread aboumt of time by doing work. We were able to determine that energy is transfered by force. In order to check out graphs we developed the equation the change in energy of the gravitational field = mg x change in height. We did a trial of the lab as a class at an angle of 90 degrees, using the equation, we found the answer to be 15, which was very close to the 16 from our classes data. From this we were able to conclude that height and energy are directly related. As height of the car increases so does the energy in the gravitational field.

8.1-8.4

smithr1313 — Tue, 26 Jan 2010 13:28:37 +0000

When a force is applied to an object which creates motion of that object work is being done. The formula for work is forceXdistance. Work is measured in Joules and can vary in different situations. Depending on the activities the same amout of work can be applied with varying distances. Power determines how long it takes to complete work and is measured in Watts. The formula for Power is the work done/the time interval. The most common form of energy is mechanical energy. Mechanical energy is energy due to position or motion of an object. Mechanical energy can be potential or kinetic energy. Potential energy is stored energy to do work. Gravitational potential energy is required to raise an object against earth’s gravitational pull. The formula for gravitational potential energy = weight x height.

11.4-11.7

smithr1313 — Sun, 10 Jan 2010 17:58:13 +0000

The resistence of an object to changes in its rotational motion is called rotational inertia. “rotationg objects tend to keep rotating, while nonrotating objects tend to stay nonrotating.” A torque is required to change the rotational state of moation of an object. The greater the distance between the bulk of the mass of an object and the axis about which the rotation occurs, the greater the rotational inertia. The formula for rotational inertia when the mass stays the same distance from the rotational axis is I=mr^2. Whenever the mass is more spread out, the rotational intertia is less, making the formula different. The rotational inertia varies with different objects because they all have varying messes and radii.Base don our lab we did in class, we learned that an object with a larger radius, will have a larger rotational intertia. The class discussed a figure skater and was able to come to the conclusion that the rotational inertia is greater when the radius is greater, so when the radius is smaller you will move faster because there is less inertia. The rotational inertia of the human body varies about each axis. Moving objects mass and velocity creates the linear momentum, and rotational inertia creates angular momentum. When a direction is assigned to rotational speed, it is called rotational velocity. The given formula in the textbook is, angular momentum=rotational inertiaXrotational velocity. Also, angular momentum= the linear momentumXradius. The law of conservation of angular momentum states that angular momentum will remain constant if an external torque does not act on the object rotating. Rotational inertia and rotational speed act indirectly. As one increases, the other decreases.

9.1-9.3

smithr1313 — Sun, 10 Jan 2010 17:37:15 +0000

An axis is a straight line around which a rotation takes place. Rotation is when an object rotates around an internal axis, revolution is when an object rotates about an external axis. There are different types of speeds for different types of motion. Linear speed is the distance moved per unit of time. Rotational speed is the number of rotations per unit of time. For example. On a record disk, all points on the record will have the same rotational speed, because they all rotate the same number of times in the same amount of time. However, a point on the outside of the disk and the inside of the disk will have different linear speeds because it takes longer for the point on the outside of the disk to move the same amount of time it takes a point on the inside of the disk. Tangenital speed is the speed of somthing moving along a circular path. Rotational speed and tangenital speed are related through the formula, tangenital speed ~ radial distanceXrotational speed. An object will have a faster tangenital speed the further is moves away form the axis it is, but the rotational speed always remains constant. Centriptal force is any force that causes an object to follow a circular path. We discussed in class and demonstrated that an object with a smaller radius will move faster than an object with a larger radius. Centripital force is what allows an object to move about an axis in the first place.

Air Resistance

smithr1313 — Thu, 03 Dec 2009 01:21:17 +0000

If an object has a constant velocity, it is safe to say there is no air resistance on the object. This is because only a large amount of air resistance affects the velocity of an object. You can see the affects of air resistance on an object in its graphs. If an object has significant air resistance, the horizontal position vs. time graph will be curved and the vertical position vs time graph will not be perfectly hyperbolic. Instead, the line will be steeper at the beginning and flatten out towards the end. By testing an object we can determine wether or not there is air resistance affecting its motion. If the object has a constant velocity, it is safe to say there is very little or no drag, however if there is an acceleration there is air resistence on the object.

3.4-3.5

smithr1313 — Sun, 29 Nov 2009 20:43:03 +0000

Chapter 3.4 begins by introducing projectiles. We just finished a projectile lab in class. The text describes the same information we discovered in our experiment. For projectiles, the horizontal velocity is constant because there is no horizontal force, however the objects vertical motion will experience an acceleration. The difference between these two motions show that they are independent of one another. The only major force acting on the object is the force of gravity, which only affects its vertical motion. The formula that shows how far an object has traveled is d = 1/2gt^2.Depending on the angle an object is thrown at, the objects horizontal range will change. This is also something we discovered with our projectile lab. Depending on the angle an object comes from, the horizontal range will change. Also we found the vertical vectors and resultants will change at each point for an object. Air resistance is what affects the shape of vertical motion. When their is greater air resistance the range is minimized. The text then begins to talk about if two angles add up to 90 degrees then they have the same ranges.

Problem #9

The motions are similiar but the graphs of the two are different. The major force acting on the two objects is gravity, however, the graph of a projectile is curved.

Problem #12

In order to achieve maximum altitude and horizontal range the slingshot should be held at a 45 degree angle. Any other angle there would be either more altitude and less range, or more range and less altitude.

Problem #35

Horizontal components are not taken into account with hang time. Once an object leaves the ground it will have the same hang time if it is shot strait up or at an angle.

Problem 36#

Even though the player is now jumping at an angle the hang time will be the same even though both vertical and horizontal components of velocity occur. Similiar to the idea in problem #35. The new horizontal range does not add to the amount of time the object is in the air.

3.1-3.3

smithr1313 — Thu, 19 Nov 2009 23:54:38 +0000

Chapter 3 begins by introducing vector and scalar quantities. A vector quantity that requires oth a magnitude and direction for a complete description. This is because it takes into account both horizontal and vertical motion. This idea was ilustrated in our class experiment with the car and the river. We first assumed there would just be a vertical motion, however we learned there was a horizontal motion as well. A scalar quantity is a quantity that is described completely by magnitude only. They do not take into account direction. An example of a scalar quantity is mass. 1 kg of sand + 4 kg of cement= 5 kg. In section 3.2 velocity vectors are introduced. A velocity vector is an arrow that represents a vector quantity. The length of the arrow represents the magnitude of the quanitity and the direction of the arrow represents the direction of the quantity. Some velocities result as a comination of two or more other velocities. Horizontal and vertical velocities combine to create a resultant which is the diagonal between the two arrows. This chapter helped to further our understanding of solving for velocities and support our theory of horizontal and vertical motion from our experiment in class.

#4-The resultant would be the diagonal of the rectangle, found suing the veritcal and horizontal arrows.

#19- You find the resultant velocity by adding the velocities together. The velocity would be 150km/hr with a headwind and 250km/hr with a tailwind.

#21- The vectors create a square. You can find the magnitude of the resultant by drawing a diagonal line through the square creating a triangle. You can then use the pythagorean theorem to find the resulting magnitude. The resutling magnitude is the square root of 20000 which = 141.421.