Dynamics Review Sheet

Dynamics Test Review
Dynamics: The study of forces that cause motion
Types of Forces: can accelerate, deform, rotate measured in Newtons (N).
Force of Gravity: force of attraction between all matter
Force of Friction: force that resists relative motion of two surfaes. Always parallel to surface in contact
Normal force: force of contact that exists between two surfaces
Applied Force: the push or pull
Tension Force: the force of a rope or a chain (can only pull)
Air resistance: caused by a fluid as an object moves through it, in still air, force is opposite to velocity in direction
Free Body Diagrams:
Sketches where an object is isolated and only forces are shown
Net Force:
The vector sum of all external forces on the object
Find the horizontal and vertical components separately
Newton’s Laws of Motion
First Law:
Objects have 3 possible states
1. Rest v=0
2. Uniform Motion v≠0
3. Non Uniform Motion v≠0 and a≠0
Inertia Law: An object remains in a state of rest OR constant velocity unless it experiences an unbalanced net external force so fnet≠0
Is a property of matter that causes it to resist changes in velocity
1. Objects at rest tend to stay in rest
2. Objects in motion tend to stay in motion
3. If an objects velocity is constant, it must have a net external force of 0 if a=0, then fwt=0
4. If an object changes in magnitude or direction, the object is experiencing a net external force greater than 0 if a≠0 then fnet=0
5. The Relationship: fnet is proportional to acceleration
Second Law:
An object’s acceleration is proportional to the net external force and is inversely proportional to its mass
Units: f=m∙a N=kg∙m/s2
Third Law
For every action, there is a reaction force of equal magnitude but opposite direction.

The Force of Gravity:
Mass: the measure of the amount of matter in an object (kg, g, tonnes)
Weight: the measure of the gravitational force acting on an object
The force of gravity is proportional to mass1 and mass2
The force of gravity is proportional to 1/r2 so therefore the force of gravity is proportional to m1+m2/r2 so we conclude that Fg=Gm1m2/ r2
G=proportionality constant of 6.67x10-11N∙m2/kg2 kg/s2=N Gravitational Field Strength: The force of gravity exerted on a 1 kg mass
Friction:
When two surfaces are in contact, microscopic connections form. The connections must be broken to allow movement, the force required to do that is friction
Friction is dependent on both the nature of the types of materials and the force and normal force pushing them together.
Friction is directed opposite of the motion of the surfaces.
Static and Kinetic Friction:
Generally, more force is needed to start an object than to keep it moving.
Static Friction: FS, is the force of friction experienced between two objects that are not moving FS ≤ µFN
Kinetic Friction: FK is the force of friction experienced between two objects as they move past each other FK=µKFN FS > FK