Journal Entry 2/14

1) The three experiments mentioned have prompted the discovery that circular motion is the result of an unbalanced force in the direction of the center of an object.
--> Bowling Ball: When the ball is rolled in a straight line, an unbalanced force is necessary to change its path of motion. Rapid taps on the side of the ball cause it to move in a circle. This tap is a force toward the center of the object. The path of motion that ensues is circular.
--> Bucket: When the bucket is swung in a circle, the water does not come out. The rope is an unbalanced force pulling on the bucket. Because the rope is pulling towards the center, the bucket moves in a circle and the water stays inside.
--> Air puck: If the air puck is turned on it will glide in a straight line. When it is attached to a string anchored to the floor, however, it begins to move in a circle. The string is an unbalanced force on the puck. Because this net force is pulling towards the of the object, said object moves in a circle.

2) When a small ball is rolled inside a ring-shaped track, the same pattern is observable. The track acts as an unbalanced force on the ball, pushing inward on this object. This causes the ball to move in a circle. The notion that the track is an unbalanced force can be tested if a piece of the track is removed. When a piece of the track is removed, the unbalanced force is removed from that portion and the ball leaves the track in a straight line.

Journal Entry 2/1 Continued

Newton's Third Law: F a on b = - F b on a

1. You are seated on a bench. The earth exerts a force on you, and the bench exerts a force on you. Do these two forces represent a Newton’s Third Law force pair? Explain.

In this situation, both forces are being exerted on me, which means they violate Newton's Third Law and cannot be force pairs.

2. A pen sits on a desk. The desk exerts a force on the pen, and the pen exerts a force on the desk. Do these two forces represent a Newton’s Third Law force pair? Explain.

In this case, the pen is object A and the desk is object B. Both are exerting a opposite force on the other, making them a Newton's Third Law force pair.

3. You pull on a rope. The rope pulls on a wagon. Do these two forces represent a Newton’s Third Law force pair? Explain.

Although there are two forces being exerted here, they are being exerted on different objects. Object A (me) is pulling on object B (rope). Object B (rope) however is pulling on Object C (wagon). These forces do not support Newton's Third Law.

4. A book slides across a tabletop. The book exerts a downward force on the table, and the table exerts a frictional force on the book opposite the direction of its motion. Do these two forces represent a Newton’s Third Law force pair? Explain.

Although there are two forces here, the book's downward force on the table and the frictional force of the table on the book, they do not correlate because one is a vertical force and the other is a horizontal force.

In my original post, I continually remarked that an object could not be moving without an unbalanced force. This is a false statement. Through recent lessons I have to come to realize that an unbalanced force is only necessary for initial movement. Once an object is in motion, there does not need to be an unbalanced force. For example, after a bowling ball is rolled and it reaches a constant speed, there is no unbalanced force on it, but it is still moving.

Journal Entry 2/7

Describe in words how the magnitude of the frictional force that the table's surface exerts on the block varies in opposition tot he forces exerted by the spring pulling on the block.

As the force exerted by the spring increases, the amount of friction exerted on the object by the surface increases. once the force of the spring overcomes the force of the friction however, both forces lessen. When there is constant motion, there is constant friction. These support Newton's Third Law which says that the Force of object A on object B is equal and opposite to the Force of object B on object A.