Ch4_WangS

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 * Chapter 4: Newton's Laws **

a) Newton's First Law

 * __What is Newton's First Law?__
 * This law states that objects have the tendency to continue doing what they are doing. This means that objects at rest will stay at rest, and objects in motion will continue moving. This, however, doe not apply in the presence of unbalanced forces.
 * __What is an everyday application of Newton's first law?__
 * If you are in a car, you can feel like you are moving even after the car has stopped. This is caused by inertia, and means that it can take some time for the the unbalanced forces to act completely on an object and cause change.

b) Inertia and Mass

 * __What is inertia? What is mass?__
 * Inertia is a resistance to change, as well as an object's tendency to keep doing what it's doing. Mass is the object that is being acted upon.
 * __Who is Galileo? What is his relation of inertia?__
 * Although many think Newton was the first scientist to come up with the idea of inertia, it was actually Galileo who did this. He also believed in inertia, and said that when objects had a tendency to stop, it was because of friction, not inertia. He said that if a ball went down a plane and up again, at the same angle, it would reach the same height almost. The difference between the initial and final heights are because of friction, not inertia.
 * __Why doesn't force keep objects moving?__
 * Eventually, friction will make an object move slower, then stop. This is why objects cannot move forever due to force.
 * __How do you measure mass as the amount of inertia?__
 * The more inertia an object has, the more mass it has, and vice versa. The less inertia an object has, the less mass it has, and vice versa. You can determine the mass of an object by it's inertia in relative form.

c) State of Motion

 * __What does the "state of motion" mean?__
 * The state of motion is determined by the velocity of an object. For this purpose, inertia could be redefined as the velocity's resistance to change. It can also be defined as the resistance to acceleration.

d) Balanced and Unbalanced Forces

 * __What makes a force balanced or unbalanced?__
 * A force cannot be balanced or unbalanced. These terms refer to the balance of the forces on the system. When two forces balance each other, it means they are of the same magnitude and in the opposite direction. When two forces are unbalanced, they either do not have the same magnitude, or are not in opposite directions. In addition to this, forces are not balanced if there is an odd number of forces. Objects that are accelerating have unbalanced forces.

Summary of Lesson 1:

 * Newton's First Law claims that objects at rest stay at rest, and objects in motion stay in motion unless they have an unbalanced force acting upon them. From this, the concept of inertia is derived. Inertia was first introduced by Galileo, and explains an object's tendency to continue doing what it is doing. Forces are balanced when they have the same magnitude and are in opposite directions, and are unbalanced when the object is accelerating, or when these two requirements are not fulfilled.

a) The Meaning of Force

 * __What is the meaning of force?__
 * A force is basically a push or pull on an object because of its interaction with another object. Forces are measured in Newtons (N), and are vectors.

b) Types of Forces

 * __What are the different types of forces?__
 * **Applied force** and **normal force** occur when two objects come into contact. **Gravity force** is the weight of an object. **Friction force** occurs when an object moves across a surface. **Air resistance force** is a type of friction. **Tension force** is only present when force is transmitted through a rope or cable. **Spring force** is the force exerted by springs when they are compressed or stretched.
 * __What is the difference between mass and weight?__
 * The mass of an object is the amount of matter it has. The weight of an object refers to the force of gravity acting upon an object.
 * __What is the different between sliding and static friction?__
 * Sliding friction occurs when one object slides on a still surface. This is different from static friction, which exists between two objects, and prevents a stationary object from moving.

c) Drawing Free-Body Diagrams

 * __What are free-body diagrams? How do you draw a free-body diagram?__
 * Free-body diagrams are vector diagrams that show the relative magnitude and direction of all forces acting upon it. To draw a free-body diagram, draw the object, without the environment, and draw and label all force arrows.

d) Determining the Net Force

 * __How do you determine the net force?__
 * To find the net force, use vector addition and find the resultant. If the resultant is 0, then that means the forces are balanced. If the resultant is not 0, the forces are unbalanced.

Summary of Lesson 2:
This lesson was all about forces, which is basically a push or pull because of the interaction between two objects. Forces can be shown in a free body diagram, which is a diagram with only the object shown, without the environment. Arrows are drawn on these diagrams, and show the magnitude and direction of different forces. The net force can be found by adding all the force vectors. When doing so, it is important to remember that vectors with the same magnitude in opposite directions cancel each other out.

a) Newton's Second Law

 * __What is Newton's Second Law of Motion?__
 * It says that the acceleration of an object is directly proportional to its net force. The equation to find net force is F=ma, and force is measured in Newtons (N). The law also says that 1 N = 1 kg * 1m/s^2.

b) The Big Misconception
Summary: Newton's Second Law of Motion states that the acceleration of an object is directly proportional to its net force. To find force, use F=ma, and use Newtons as your unit. Although many people think that to keep moving, an object needs to have force applied it, this is inaccurate. In reality, friction, a force, helps slow down objects and helps them stop. Also, if only weight and normal height are labelled on a free body diagram, the object can be moving horizontally, and doesn't need to be at rest.
 * __What is the big misconception about Newton's Second Law of Motion?__
 * Many people have the misconception that forces are needed to keep an object moving. However, this is not true. To move, an unbalanced force first needs to act on the object. If no forces acted on the object after that, it would keep moving forever. To stop, objects need the presence of friction, a force, to act on them. Another misconception that confounds many involves free body diagrams. When some people see a free body diagram with only weight and normal force indicated, they think that the object must be at rest. However, the object can also be moving horizontally. This is hard for many people to believe.

**Vectors- Lesson 3**

 * __What happens to net force if it is applied at an angle?__
 * When a force is applied at an angle to the horizontal, it can be split into two components, an x and a y. These two components are equal to the force at an angle. By doing this, all forces are either horizontal or vertical.