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Unit 2: Dynamics – Newton’s Laws of Motion
Essential Questions
How is knowledge of the net force essential to understanding an object’s constant velocity?
When the net force is zero, the acceleration of an object is zero, meaning the object is either at
rest, or moves at a constant velocity.
How does the presence of a net force determine the acceleration of an object? What is the
nature of friction and how does it factor into an object’s acceleration?
The net force will cause an object to accelerate, and the acceleration is proportional to the net
force, and inversely proportional to its mass.
Friction is parallel to the interacting surface and normally will reduce the net force, causing
acceleration to be lowed. If present, it must be included when calculate the net force.
What are action-reaction force pairs? And do they cancel each other? Why or why not?
Can an object exert a force on itself?
A force is an interaction between 2 bodies. For every action, there is an equal and an opposite
reaction. Action and reaction can’t cancel each other because it’s one force between 2 bodies.
Only 2 forces acting on 1 body may cancel each other. An object can’t exert a force on itself.
How can free-body diagrams be used to create a mathematical representation of the forces
acting on an object?
Free-body diagrams can be used to identify all the forces acting on an object. When all the forces
in every direction are balanced out, the object’s motion will not change. If there is unbalanced
force in any direction, the object will accelerate in that direction.
How can you utilize Newton’s laws of motion to predict the behavior of objects? How do
Newton’s laws apply to systems of two or more objects?
In the absence of a force, or when the net force acting on an object is zero, the object’s motion
will not change – it either stays at rest or moves at a constant velocity (first law).
When net force acting on an object is not zero, the object’s motion will change – its acceleration
is directly proportional to the net force, and inversely proportional to its mass (2nd law).
When there are 2 or more objects in a system, Newton’s laws applies to the whole system, and
also applies to each object in the system.