Unit 2: energy & momentum Flashcards
work
done on an object when a force acts on the object, causing the object to move in the direction of the force
what happens if the force and displacement are not in the same direction
the component of the force that is in the direction of the
displacement must be used.
positive work
- applied force acts in the same direction as the motion (θ lies between 0 ̊ and 90 ̊)
- energy is added to an object
- final energy is greater then inital energy
negative work
- applied force acts opposite to the direction as the motion (θ lies between 90 ̊ and 180 ̊)
- force causes the object to lose energy
- final energy is less then inital energy
zero work (ex.1)
When the applied force is perpendicular (90 ̊) to the
displacement of the object.
Ex) carrying a textbook across the room
zero work (ex.2)
When the applied force is equal to zero.
Ex) on object travelling through space at a constant
velocity
zero work (ex.3)
When the displacement of the object is zero.
Ex) pushing on a wall
zero work (ex.4)
When an applied force creates Circular Motion.
Ex) keys spinning in a circle (F is perpendicular to the
motion)
Work – Energy Theorem
the work done to an object by an external force is equal to the change in its kinetic energy
Isolated Systems (Closed)
a system that cannot interact or exchange energy with external systems (its surroundings)
Open Systems
a system that can interact with another external system and exchange energy with its surroundings
Elastic Object
an object is said to be elastic if it returns to its original or normal
shape after a deforming force is removed
ex) a sling shot, elastic band, trampoline, strut on a car
Inelastic Object
object doesn’t return to its original shape
Hooke’s Law
the amount of force exerted by a spring is directly proportional to
the displacement of the spring
Perpetual Motion Machines
- this is a device that can operate for an unlimited amount of time without outside help (restarting or refueling)
- these machines cannot be created in the real world as some of the mechanical energy will always be lost from the system as thermal energy, sound energy, or other forms of energy.
