QOD: Suggest why placing wheels under a heavy box reduces the necessary force required to push it along at a constant speed.

Transcription

1 QOD: 2 22 Suggest why placing wheels under a heavy box reduces the necessary force required to push it along at a constant speed. Feb 21 3:05 PM 1

2 force: any action that can affect the motion of an object. Make a chart comparing the four fundamental forces. Include in your chart the relative strength of each and the effects of each. The four fundamental forces are gravity, the electromagnetic force, the strong nuclear force, and the weak nuclear force. Feb 21 2:52 PM 2

3 The strong and weak nuclear forces act over only short distances. These are the forces that hold atoms together. The strong and weak nuclear forces are important, but you do not experience them directly in your everyday life. The force of gravity and electromagnetic forces are forces you feel every day. Gravity acts over long distances and pulls objects toward each other. Electromagnetic forces produce friction, magnetism, and static electricity. Feb 21 2:56 PM 3

4 The strong nuclear force is the strongest of all the forces. The strong nuclear force holds together the protons and neutrons in the nuclei of atoms. However, it only acts over short distances. The maximum range of the strong nuclear force is about the size of an atomic nucleus. Feb 21 2:57 PM 4

5 The weak nuclear force is about ten trillion times weaker than the strong nuclear force. The weak nuclear force affects some kinds of radioactive decay. Feb 21 2:58 PM 5

6 Electromagnetic forces can act over longer distances and are about 1% of the strength of the strong nuclear force. Electromagnetic forces hold electrons near the nucleus of an atom and hold molecules together. Feb 21 2:58 PM 6

7 Gravity is the weakest of the fundamental forces. It is about 1040 times weaker than the strong nuclear force. It also works over longer distances than any of the other fundamental forces. Gravity is an important force in shaping the structure of our galaxy and the universe. Feb 21 2:59 PM 7

8 Forces can act through contact or at a distance. If you push a cart, the cart moves. When you catch a ball, it stops moving. These pushes and pulls are examples of contact forces. There is another class of forces called field forces that do not require that the objects touch each other. The attraction of gravity or the repulsion between two north poles of a magnet are examples of field forces. Both contact and field forces can cause an object to move or to stop moving. Feb 22 7:18 AM 8

9 How Can Forces Affect Motion? Forces act to change the motion of an object. In most situations, several forces act on an object at once. The net force is the combination of all the forces acting on an object. An object will accelerate in the direction of the net force. An object will not accelerate if the net force is zero. Feb 21 3:00 PM 9

10 Balanced forces produce a net force of zero. Therefore, an object experiencing balanced forces will not change its motion. Feb 21 3:02 PM 10

11 Unbalanced Force: When the net force acting on an object is greater than zero, the object will accelerate in the direction of the net force. Feb 21 3:03 PM 11

12 1. Make a holder for 50 marbles with a plastic cup and string. Tie the string around the wood block. 2.Put a 20g weight on the block and place the wood on top of a sheet the different sheets lying on a table. Hook the string to the cup and hang it over the edge 3. Add marbles to the cup until the block of wood begins to move. 4. Repeat the process using different surfaces, such as sandpaper, notebook paper, and the bare table. Feb 22 7:07 AM 12

13 Cork Rubber Sand Paper Table Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Post Lab 1.Is the number of marbles needed to start moving the block the same for each type of surface? 2.Relate the number of marbles used in each trial to the roughness of the surface. Feb 22 7:09 AM 13

14 Feb 21 3:04 PM 14