Unit 4 Blog

    In Unit 4, the first think that we learned about was about rotational motion and how the circular motion can be defined as either tangential or rotational and how those two correlate. The definition of tangential speed is the direction of the motion tangent to the circumference of the circle. We learned that tangential and and linear speed can be used interchangeably. Rotational speed, however, involves the number of rotations or revolutions per unit of time. We used these two definitions with many everyday problems and scenarios that correlate appropriately. The real life exercise we used was the merry go round question. All of the fine physics students in Ms. Lawrence's class embarked on a journey to the outside world, were we lined up and locked arms. We learned now that even though the inside center point of the rotating line, trying to represent the merry go round, the students who were on the out side of the line were moving at a faster speed in order to cover the same ground as the students on the inside. This is due to the fact that they have the same rotational speed because they are connected, but have different tangential speeds because the outside needs to cover more distance than the inside.


 
   The next thing we learned about was rotational inertia. Rotational Inertia is the property of an object to resist changes in its rotational motion. Like inertia for linear motion, rotational inertial depends on mass and where it is positioned in accordance to the axis of rotation. The real life example we used in this case was the idea of a spinning ice skater. When the Ice skaters arms are out wide spread from her body she begins to slow down because her mass is distributed farther away than her axis of rotation. When the ice skaters arms are inward she is bringing her mass closer to her axis of rotation which allows her rotational velocity to increase varying proportionately.

    The next topic our clever physics students embarked upon was the concept of torque. A torque is the rotational counterpart of force. Torque acts on a force and tends to twist or change the state of motion when force is acting on that object. We learned that torque can mathematically be calculated by Torque= force x leverarm. In this case we learned to calculate the weight of a meter stick by using this equation. The lab that I participated in helped me understand the questions that were on the test. The lab consisted of  balancing the meter stick on a fulcrum (edge of the table) with a 1N force acting on it. and our goal was to calculate the mass without using the scale. We found this finding each lever arms and balancing the torques.



Following the concept of torque we leaned about center of mass and center of gravity. The center of mass can  be looked at by being the point where an object wobbles when off balance. Center of gravity is a term popularly used to describe the center of mass. They share the most common of relevance. The question that was asked in class, was why is it easier to push someone over that is standing straight up rather than in a squatting position. Well, this is because when the feet are in a squatting position then its center of gravity is inside its base of support causing it to have equilibrium.



The last thing we learned about was about centripetal force. Centripetal force is any force that is directed inward on a fixed center of an object. Centripetal is another name for "toward the center" or "center seeking." The example Ms. Lawrence used in class was rotating a plate with strings on it and a cup of water resting on it and twirled it around in a circular motion. In this case, the strings had centripetal force acting on them and the cup of water was pushing out ward.