Unit Two Content
This unit, we focuses on different types of forces and applying them into force problems. We used the Newton's laws, as well as system schemas and free body diagrams, to help us solve these problems.
Newton's Second Law
Newton's second law is net force equals acceleration times mass. Both net force and acceleration are vectors, meaning they have both magnitude and direction. You can rearrange these variable to solve for net force, mass, and acceleration if you have the other two variables.
Newton's Third Law
Newton's third law is for every force from object 1 to object 2, there is an opposite but equal force from object 2 to object 1. These two forces are commonly referred two as Newton's Third Law Pairs. A common misconception is that normal force and the force of gravity are Newton's Third Law Pairs.
Newton's first law, or the law of inertia, is an object will move at a constant velocity unless it feels an unbalanced push or pull. 0 m/s is still a constant velocity pertaining to this law. Inertia is the resistance to acceleration
Newton's First Law
System Schemas
With system schemas, you can identify all the forces acting on the object of interest. With every object there is an acting force of gravity that is always acting down. if the object is moving, there will most likely be a force of friction acting in the opposite direction. With a normal force, there will usually be a force normal actin upon it, which is equal in magnitude but perpendicular to the applied for of the object, so usually opposite of the force of gravity.
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https://www.compadre.org/nexusph/course/Using_system_schemas_for_Newton%27s_3rd_law
Force Diagrams
Force diagrams illustrate the direction and magnitude of objects acting upon the object of interest. The force of gravity is always down, and usually the normal force is opposite the gravitational force (perpendicular to applied force). With any applied force, the force of friction will be opposite to it, but less in magnitude.
Force Calculations and Force Problems
In order to solve force problems, you use the main two equations of Fg = mg and F=ma to calculate the net force using a force diagram, a system schema, and a force table, a table which calculates the x and y values of the forces. You can usually calculate the force of gravity, which is equal to the normal force, and calculate the net force from there, and therefore find the acceleration.
Relating Representation of Motion and Force Models
Motion models usually only show the applies force happening, and a drawing of the object of interest. gravity, normal force, and usually friction cannot really be seen in a motion model. Sometimes you can see the friction if there is a lot of it. For force models, you account for all the forces acting upon this object, invisible or visible. You will normal have 4 forces in force models, modified to the angle its acting on. Remember that gravity is always down, the normal force is perpendicular to the applies force, and the frictional force is opposite the applies force.
Solving Problems With Forces and Motion
Example Problem: Two physics students team up to move a huge box. The box has a mass of 110 kg. each student pushes with a force of 155 N. The box moves at a constant velocity to the right. Identify the forces on the box.
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