Work, energy, and power Flashcards
(19 cards)
Define energy:
the ability to do work; a quantitative property transfered to a body or system (J)
Define work done:
the transfer of energy (J); fscosx for a constant force
Work done is also the change in energy.
F is force, s is displacement, x is angle of the force relative to the angle of displacement
Define power:
amount of work done over time
No work is done if:
- no force is applied
- cosx is 0 (x is 90)
- no displacement (e.g. pushing on the wall means no work done on wall, yes work done on muscles)
If work is positive, _
If work done is negative, _
- Energy is increasing; the object is moving faster and higher (Fnet exists)
- Energy is decreasing; the object is moving slower and lower
Define momentum (P):
Inertia in motion; P = mv (kgm/s)
More momentum means:
More force is needed to slow the object down
Define impulse (J):
Change in momentum; J = Ft = P2 - P1
Define elastic potential energy (Ep):
Potential energy stored as a result of deformation of an elastic object, such as the stretching of a spring
kx^2/2
Define gravitational potential energy (Eg):
the change in the kinetic energies of the objects as they fall towards each other. Gravitational potential energy increases when two objects are brought further apart and is converted to kinetic energy as they are allowed to fall towards each other.
mgh
Conservation of energy states that:
the total energy of an isolated system remains constant. energy cannot be created nor destroyed, only converted.
Ek1 + U1 = Ek2 + U2
In a force-displacement graph, the area underneath is:
In a force-time graph, the area underneath is:
- work done
- impulse
Conservation of momentum states:
the total momentum of a system is constant, unless acted on by an external force
m1v1 + m2v2 = m12v12 + m22v22
Types of interactions between objects in a system:
- hit and stick: inelastic collision
- hit and bounce: elastic collision
- explosion (objects start together, then separate)
Elastic collision spectrum:
Perfectly inelastic: objects become one mass. as much kinetic energy as possible is lost to heat and sound. (car crash)
Inelastic: kinetic energy is lost, but objects usually remain separate
Elastic: all kinetic energy is approximated saved (soccer ball and foot)
non-kinetic energy and momentum are always preserved.
Glancing collision define:
Colliding objects do not go in the same directions they came from. The most realistic type of collision; x and y components must agree before and after
Gravitational potential energy in space?
-GMm/r
Launch velocity vs. orbit velocity:
Launch velocity is the velocity required to leave the surface of the planet. Orbit velocity is the velocity required to stay in orbit.
Consider a system with friction. Explain the relationship between work and mechanical energy.
Mechanical energy (final) - mechanical energy (initial) = work done by friction (negative value)
