Monday, February 22, 2010


Part A:
 This is what i have learned about energy:

There are many different types of energy. Some of them are potential energy, elastic potential energy and kinetic energy. Potential energy is the stored energy of position obtained by an object. What that means is that an object gets stored energy by where the object is placed. For example, the wrecking ball has stored energy when it is held up at an elevated height. The equation is PE= mgh. The units are in Joules (J). Elastic Potential Energy has to do with elastic materials. An example of elastic potential energy would be a bungee jumper jump of a cliff. This type of energy happens when elastic materials are stretched or compressed together. The equation would be PEe=1/2kx^2. Lastly, an object that has motion will also have kinetic energy. The equation for Kinetic Energy would be KE= 1/2mv^2. This equation means that the kinetic energy of an object is directly proportional to the square of its speed.

What I have found difficult about energy is the conservation of mechanical energy. I would say that this topic is hard because I was sick and missed the lesson and the notes about it. I have some questions and there are certain concepts that I do not understand fully.

I feel like my problem solving skills are still strong. However, there will always be weaknesses in my problem solving skills. Sometimes there are certain equations that do not give the answer straight forward so you have to figure out which equations to use.

Part B:

While I am driving down the highway 635, along with other drivers, the kinetic energy equation can help me figure out how much kinetic energy my car obtains. For example, A 900-kg compact car moving at 60 mi/hr has approximately 320 000 Joules of kinetic energy. Estimate its new kinetic energy if it is moving at 30 mi/hr. The KE is directly related to the square of the speed. If the speed is reduced by a factor of 2 (as in from 60 mi/hr to 30 mi/hr) then the KE will be reduced by a factor of 4. Thus, the new KE is (320 000 J)/4 or 80 000 J.

car in motion

Monday, February 1, 2010

The Physics of Rollerblading and Friction

Have you ever wondered…what caused a person wearing rollerblades to start forward when they are at rest or how does the friction occur between the skates and the ground??? Well in order for the in-line skater to begin moving, he or she must experience a force in the direction of motion which causes her to accelerate from rest to some velocity. An inline skater at rest is only exerting a force down upon the ground (gravity) and the ground is exerting an opposite but equal force up on the skater. All four wheels of the rollerblade are in contact with the surface. The wheels begin to rotate due to the frictional force (static friction) between the wheels and the surface. The static friction exerts torques on the wheels which makes them spin. In order to eliminate any sliding friction, the rollerblade wheels rotate using a ball bearing system. To get a full grasp on the friction and rollerblading click on the link below.

Rollerblading and Friction Fun!!!