UNIT 2: FORCES
Brief Overview
When you think about what is keeping you on this floating ball in space and keeps you from flying off into space you may think of Earth science or physical science. However, Physics is the reason that you are not sinking into the ground or floating into space. Specifically, the forces objects have on each other and Newton's laws of motion explain this.
TERMINOLOGY
FORCE OF GRAVITY
The Force of Gravity is the gravitational constant multiplied by the mass. It is always negative and its vector representation always points down.
NORMAL FORCE
Normal Force is the Newton's 3rd law pair of the Force of Gravity. It is calculated by weight multiplied by the gravitational constant. Always perpendicular to the surface object is on.
FRICTION FORCE
Distance is the actual amount the object has traveled. So if a cyclist biked 10 miles, even if it was a roundtrip, his distance would be 10 miles.
NEWTONS LAWS OF MOTION
LAW OF INERTIA
Newton's first law of motion, the law of inertia states that the state of an object will remain constant unless something acts on it. Also states that the inertia of an object is dependent on its mass (larger mass - larger inertia)
LAW OF MASS AND ACCELERATION
Newton's second law of motion states that the acceleration of an object is directly proportional to the force exerted on it and is inversely proportional to the mass of the object.
NEWTON'S THIRD LAW OF MOTION
Newton's third law of motion states that for every force applied, there is an equal and opposite reaction. This law introduces third law pairs such as normal force and gravity.
https://www.biography.com/scientist/isaac-newton
IDENTIFYING INTERACTIONS
System Schema
A System Schema is a picture description of the problem in the question. A system schema is a diagram with the objects in the problem connected by arrows representing the forces acting on each object. It is incredibly useful in that it puts the problem in a form that is much easier to understand.
FORCE CALCULATIONS
NET FORCE = MASS * ACCELERATION
This equation is super important and is incredibly helpful in solving Force Problems. This equation can be used to find the net force, acceleration, or mass. You can modify the formula as a = f/m or m = f/a. Another way to find the net force however is just to add up all the forces.
FORCE TABLES AND FORCE DIAGRAMS
Force Tables and Force Diagrams are extremely useful in force calculations. Force diagrams show in which direction each force is acting in relation to the object. Force tables are a useful way to organize all the information that you have and to calculate missing parts.
https://www.physicsclassroom.com/class/newtlaws/Lesson-2/Drawing-Free-Body-Diagrams
RELATING REPRESENTATIONS OF FORCE MODELS AND MOTION
POSITION TIME GRAPH
This position-time graph shows us the actual trajectory and position of the object. From this graph we can infer that the object in question is being thrown into the air and returning to the ground
VELOCITY TIME GRAPH
To find the velocity graph you can take the derivative of the position-time graph. Since this Velocity time graph is a negative sloping linear line that crosses the x-axis we can infer that it is an object that starts with a high velocity and then slows down until its x-intercept after which it speeds up again.
ACCELERATION TIME GRAPH
The acceleration graph can be found by taking the derivative of the velocity graph or the second derivative of the position-time graph. In this scenario, we can see that the acceleration is constant.
SOLVING PROBLEMS WITH FORCE AND MOTION
CW: they look hard
Seeing Problems with many moving parts and no numbers may seem extremely confusing and difficult at first, however, you have to take it piece by piece so you know exactly what you are doing. First, you want to create a system schema so that you know what forces are present in the problem. Then, you create a force diagram so that you know in which direction each force is acting in relation to the object. Finally, when you solve the problem you first want to create a force table and then look to see which formulas will make it the easiest to solve for the variable you need.
