Brief OverviewForces: A force is a push or pull upon an object resulting from the object’s interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. In this unit, we explored the different types of interactions between objects. We learned about the different forces that occurred, and how to calculate them. We learned how to interpret the direction and magnitude of force, and how that resulted in either a balanced or unbalanced net force.
Image: https://easyscienceforkids.com/wp-content/uploads/2013/06/push-and-pull-e1449475314339.jpg |
Newton's Third Law:Whenever there is an interaction between two objects, there is a force upon each of the objects. These two objects each feel the same magnitude force from the other, but in the opposite direction.
Forces are a mutual push or pull between two objects. Each of these forces is half of a 3rd Law Pair. Image: https://stickmanphysics.com/wp-content/uploads/2020/10/Newtons-3rd-wall.jpg |
Identifying Interactions: System Schemas and Force Diagrams:System Schemas: They are a visual way to keep track of the objects in a system and how they interact. Each object is a circle. Every force is a line connecting two circles. If it is a contact force, the line is solid, and if it is non-contact, then it is dashed.
Force Diagrams: Force diagrams show both direction and magnitude, unlike a system schema. The object of interest is labeled as a dot. An arrow is then drawn from the dot for each force acting on the object, in the direction that the force is acting. Each force is then labeled by its type by the other interacting object on the object of interest. Image: https://www.frostphysics.org/uploads/3/8/3/5/38359885/screen-shot-2019-01-23-at-3-48-46-pm_orig.png |
Force Calculations:Force of Gravity: Fg= m*g. The force of gravity depends on the mass, m. The constant is the gravitational field, g, which on earth is 9.8 N/kg.
Spring Force: Fs= -k*△x. The spring force depends on how much the spring is stretched or compressed, △x. The constant is the spring constant, k, which is a measure of the spring’s stiffness. Force of Friction: Ff = μ*FN. The force of friction depends on the normal force, FN. The constant is the coefficient of friction, μ, which often indicates surface roughness. Image: https://www.wikihow.com/images/thumb/0/01/Calculate-Force-Step-2-Version-2.jpg/v4-460px-Calculate-Force-Step-2-Version-2.jpg |
Solving Force Problems:Solving a force problem begins with identifying all of the known information. To clarify this for yourself, you would draw out a system schema, force diagram, and force table. You would then be able to see all of the different forces acting on the object, and whether it is balanced or not. You can then calculate our unknown force using the force calculator equations, as well as common sense. For example, if the only forces affecting vertical motion are the normal force and gravity force, and gravity force = -200 N, and the object has no vertical movement, then we can assume the normal force is 200 N, as the forces are balanced. If a force is moving in a diagonal direction, we can use trigonometry to figure out the vertical and horizontal components of the force, as after all forces are vectors.
Image: https://www.wikihow.com/images/thumb/b/b0/Calculate-Force-of-Gravity-Step-10.jpg/aid1626695-v4-1200px-Calculate-Force-of-Gravity-Step-10.jpg |
Relating Representations of Motion and Force Models:A force diagram is very useful, as unlike a system schema, it represents both the direction and magnitude of a force. It depicts all of the acting forces involved in the motion of the object. More specifically, it shows the acceleration of the object, because F=ma. By showing whether or not the forces are balanced, we can figure out whether or not the object is accelerating, or simply moving at a constant velocity.
Image: https://excelschools.net/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics-600.png |
Solving Problems with Force and Motion:
Solving problems with force and motion starts with us making our force tables. We then fill in what we know, and calculate what we don’t. We should also list all of our known variables for our kinematic equations, so we know which one we should use. Once we have calculated our forces, we know that Net Force = mass*acceleration. From there, we can solve for acceleration, which is another variable for our kinematic equations. Hopefully at this point we will have enough information to solve whatever the problem is asking.
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