Momentum and Impulse Flashcards
What is momentum? What equation can be used to calculate momentum?
Momentum is the product of an object’s mass and velocity.
p = mv
- Direction is same as velocity
- Units are dependant on units for m & v
What is Newton’s 1st Law of Motion described in terms of momentum?
An objects momentum will remain constant until it is subjected to an external net(unbalanced) force.
What is Newton’s 2nd Law of Motion described in terms of momentum?
An object’s momentum will change when subjected to an external net force over a specific time interval.
How can we derive the equations of impulse from Newton’s 2nd Law of Motion?
(Sum of)F = ma
a = (change in) v (change in) /t
(Sum of)F = (m (change in) v) / (change in) t
(Sum of) F = (Change in) p / (change in) t
(Change in) p = (Sum of) F (change in) t
_______(1) momentum is ________(2) when objects collide in an ________(3) system. ________________(4) is not conserved during collisions.
(1) Total
(2) Conserved
(3) Isolated
(4) Kinetic Energy
What can be used to calculate impulse when the net force is variable?
Net force (y-axis) vs. Time (x-axis) graphs
- the area between the function and the x- axis is equal to the impulse provided to the object
- Area must be definite
BE CAREFUL OF NEGATIVE AND POSITIVE IMPULSE: If graph is above or below x-axis, the object will have positive or negative impulse. The direction will be the same as the net force.
What is the definition of impulse? What is impulse a product of?
Impulse is the CHANGE in an objects momentum. It is the product of the net force acting on an object over a specific time of interaction.
(If object is accelerating, velocity is changing, momentum is also changing, and thus the object has impulse)
What two equations can be used to calculate impulse?
(Delta) p = (Sum of) F (Delta) t = m (delta) v
UNITS MATTER: N x s or Kg x m/s
Direction is the same as the net force
Equations can ONLY be used if the object is subjected to a constant net force.
When impulse provided to an object is constant, devices can be designed to _______(1) the net force acting on an object by ________(2) the interaction time for a collision. F is _________________ (3) to t when impulse is constant.
(1) Decrease
(2) Increasing
(3) inversely proportionate
(Sum of) F = (delta) p / (delta) t
What is Newton’s 3rd law of motion described in terms of momentum?
If object 1 exerts a force F12 on object 2, object 2 will exert an equal and opposite reaction force F21 on object 1
What is the law of Conservation of Momentum? What key physics principle describes conservation of momentum?
The total(or net) momentum of a closed, isolated system before and after a collision is constant.
Key physics principle #4:
(delta) p1 + (Delta) p2 = 0
What is a closed system?
Closed: no Mass can enter or leave the system
What is an isolated system?
Isolated: No external forces act on the system and no energy enters or leaves the system
- Main ones: Friction or an external applied force.
Show how to go from key physics principle #4 to (Sum of) Pb = (Sum of) Pa
(Delta) P1 + (Delta) P2 = 0
(P2a - P2b) + (P1a -P1b) = 0
P1b + P2b = P1a + P2a
(sum of) Pb = (sum of) Pa
What is an elastic collision?
Net momentum and kinetic energy are both conserved during a collision.
What is an inelastic collision?
- Only net momentum is conserved during a collision and kinetic energy is lost
- Whenever kinetic energy changes in a reaction, the reaction is inelastic
- Some kinetic energy is lost in the form of heat and sound
What is a purely inelastic collision?
- Objects stick together after a collision
- Kinetic energy is lost as energy is required to deform the objects
- Example: bullet and pendulum
What is an explosion?
- Has to be inelastic since kinetic energy is changing
- Initial object breaks into multiple pieces
- Kinetic energy is gained as chemical potential energy is converted into kinetic energy
How do you calculate % change in kinetic energy of a reaction?
%(Sum of)Ek change = l(sum of) Eka - (sum of) Ekbl
—————————————— X 100%
(Sum of) Ekb
What are the two key states in a collision?
Immediately before and after the collision
When is net momentum not conserved?
When the system is not closed or isolated.
