### Unit 3: Forces

Summary
This unit was about forces, both balanced and unbalanced. A force is any push or pull, and is  measured in Newtons (N). One type of force is the force of gravity, or weight (W or Fg). It is calculated by multiplying mass of an object and acceleration due to gravity (g), or 9.8. Mass (m) is the measure of the amount of matter an object contains. It is measured in kilograms. Weight and mass are not the same. The weight of an object changes depending on the how strong the gravitational pull is, but the mass of an object remains constant everywhere. Another type of force is tension force. Tension force (T) is a force that is transmitted through string.
In balanced forces, all forces cancel out. Therefore, the net force (Fnet) is always 0. When calculating balanced forces with tensions at angles, the force of gravity is equal to the y components of the two strings. In unbalanced forces, the object is moving in the direction of the greatest force. The object is also accelerating (see Newton's second law of motion below).
This unit was also about Newton's Three Laws of Motion. The first law states that an object at rest will remain at rest and an object in motion (with constant velocity) will remain in constant motion unless there is an unbalanced force. Usually, the unbalanced force is friction (f). Friction is a force that works against the motion of an object. There are two types of friction, static and kinetic. Static friction (fs) prevents the object from moving and adjusts until it reaches a maximum. Kinetic friction (fk) is the friction on a moving object. The coefficient of friction is measured on a 0 to 1 scale, with 1 representing the most friction. The coefficient of friction can be calculated with the formula: f=μFNμ is the coefficient of friction and FN is the normal force. Newton's second law of motion states that force equals mass times acceleration. Newton's third law of motion states that for every action, there is an equal but opposite reaction force.

Progress
One thing I found "easy" about this unit was Newton's three laws of motion. I remember learning all of them in 6th grade. One thing I struggled with was forces on an angle. It was hard to imagine how to calculate it until the forces were put on a coordinate grid and flipped so the x axis was horizontal and the y axis was vertical. As seen below, I gave myself a 2.5 on the first quiz because I did not understand how to calculate tension forces. However, by the end of the unit, I understood the concept and gave myself a 4 on the last quiz.

#### Unit 3 Objective Sheet Zheng

Example
This is my Friction Lab. In this lab, the coefficient of maximum static and kinetic friction was calculated for 5 different shoes. This lab demonstrated an understanding for the unit by using the mass, static, and kinetic friction of a shoe to calculate the normal force, and as a result, the coefficient of static and kinetic friction. Because the lab allowed multiple calculations and used many pieces of data to obtain the coefficient of static and kinetic friction, the lab is a good example for understanding the unit's concepts.