Physics with blogger

Now let's talk about Force. On several previous lectures, I mentioned it frequently. It's a very important physical quantity. Yes, it's a kind of physical quantity. In physics, Force is vector physical quantity. Force has magnitude and direction. Please study vector calculate through below links. Vector calculations are very important in science. http://www.mathsisfun.com/algebra/vectors.html http://www.mathsisfun.com/algebra/vectors-dot-product.html http://www.mathsisfun.com/algebra/vectors-cross-product.html Force makes some changes for the status of an object. Because of force, something can be broken. The shape of an object might be changed. We can imagine the phenomena due to force. But in physics, the definition of force is a little unique. I will express it by mathematics. F = ma Force is mass times acceleration. Consequently force is related with acceleration. And fore is the source of acceleration. Where there is acceleration there is forc...

An object in 2 Dimension motion is the one that is moving on plane. Let's assum a student thrown a ball to the sky with 30 degree angle from horizontal line. And the initial magnitude of velocity is 50 (m/s). See below image. We can make a plane for the ball's motion like x-y 2 dimensional coordinate. It looks more complecated than one dimensional motion. But there is nothing to scare. We can divide 2-D motion into two 1-D motion. If something moves like 3 Dimension motion, for example, a bird's movement, we can divide it three 1-D motions. As we see the Figure, we can divide it by x-direction motion and y-direction motion. Or we can say that one is for horizontal motion and another is for vertical motion. x direction motion is constant velocity motion. On the other hand, y direction is constant acceleration motion. Constant velocity means the motion's acceleration is 0 m/s2. We can say that the x direction motion has constanct acceleartion,...

I told you that usually there are 3 tools to describe physical phenomena. (1) Mathematics (2) Units (3) Graph This time I will use graph a lot for motion of upward. Let's see below situation on Figure 6-1. Figure 6-1   It's similar with Figure 5-1. Only different one is velocity. The initial direction of velocity is opposite with gravitational acceleration. And I will set initial position by 0. So the ground position is (-) 500 m. Guess the motion of the ball. It's not difficult to understand its motion. It will sour up to the sky. While it goes upward, the speed ( magnitude of velocity) becomes slower gradually. After all it will stop on the proper height. HW1) What is the displacement of the ball when it stops on the proper height? And at the moment, what is the taken time from the initial position ? However after at that time, what will happen to it? Yes, it will goes down like free fall motion. After at that time, we can regard it as motion of fall...

Now the initial velocity is not 0 m/s. The ball can get 2 kind of initial non-zero velocity. One is downward direction velocity and another is upward direction velocity. Let's see in the first case. The situation for the ball was changed. All situation is described on the Figure 5-1. Figure5-1 Even the ball has initial velocity,the motion is one dimensional constant acceleration motion. I will give you several problems for homework. HW1) Find out the velocity when the ball reached the surface. HW2) How long will it take to reach the surface from the top. HW3) After 2 second, describe the displacement of the ball. I hope you can solve them easily. When you meet troubles, review previous lectures. All solutions are there for this homework. Good luck.

Motion in one Dimension 4 - motion of free fall There is another theme for one Dimensional motion. Figure4-1 A man is holding a ball on the top of the building. The height of building is 100 m. Now he set it free from his hand softly. He did not throw it to downward. Just set it free by spreading fingers. Then the ball falls freely. Of course, there is no resistance. No air resistance, No wind. We know this phenomena in our life. The ball will get speed gradually as time goes. Why is it faster continuously? Maybe most of you know the reason. The reason is that because of gravity the ball is faster more and more. We will discuss about the gravity issue later. Why does it become faster gradually? The speed, the magnitude of velocity is changing with respect to the rate of time. What is the root for the change? Anyway there is acceleration. For making acceleration, we need physical force. What forces are there on the ball. It's gravitational force. Because of gravi...

Motion in one Dimension 3 - acceleration Figure3-1 Again we came back to the above situation. Don't you have any questions about it? No? Nothing? Then I will ask a question to you. The driver really can come to his home safely? Will he see his wife and children and then take dinner with them? What do you think about it? No. With above physical conditions he never enter the house safely. Because before enter home, the car need to be stopped. What should he do? Yes. He have to step break pedal to stop moving. Today let's look into the motion in break on. I will re-arrange the car's situations like below. Figure3-2 He stepped break pedal softly and continuously. So the speed became smaller gradually. In other words, the magnitude of velocity is going down gradually until it's stopped. But the direction of Velocity is (+) direction. Anyway the velocity is changing now. We've checked the definition of acceleration. Let's set the magnit...