Momentum, Impulse, and Collision Flashcards
Characteristic of motion that describes how difficult it would be to stop the moving object; vector quantity
same direction as the velocity
Momentum
SI unit for momentum
kg⋅m/s (equivalent to N⋅s)
momentum formula
p = mv
T or F. Greater momentum → easy to change its state of motion
F. Greater momentum → hard to change its state of motion
T or F. Lesser momentum → hard to change its state of motion
F. Lesser momentum → easy to change its state of motion
How to change an object’s momentum?
- apply a force
- apply the force at a longer period of time
Change in momentum of a particle during a time interval equals the impulse of the net force that acts on the particle during that interval; vector quantity
Impulse
Is the direction of impulse the same or different as the net force ΣF?
The direction of impulse is the same as the net force ΣF.
SI unit for impulse
N ⋅ s (equivalent to kg ⋅ m/s)
Impulse-Momentum Theorem formula/equation
J = ∆p = ΣF(t_2 - t_1)
What do airbags and seatbelts in cars do?
increase the time of collision
theorem which states that changes in momentum are due to impulse; changes in momentum are due to time over which the force acts
Impulse-Momentum Theorem
J = ∆p = ΣF(t_2 - t_1)
theorem which states that kinetic energy changes when work is done; total work depends on distance over which force acts
Work-KE Theorem
W = KE_2 - KE_1 = F(d_2 - d_1)
T or F. Conservation of Momentum is important in situations when 2 or more bodies interact.
T
Forces that the particles of the system exert on each other
internal forces
forces exerted on any part of the system by some object outside it
external forces
How can you say if a system is an isolated system?
if there are no external forces and F_int ««_space;F_ext
How does the total momentum of the system become constant?
if the vector sum of the external forces on a system is zero
total momentum of a system
p = p_A + p_B
Impulsive forces in a collision leave the total momentum of the system ____________.
unchanged
conservation of momentum formula
mAvA1 + mBvB1 = mAVA2 + mBvB2
A’s, B’s, and the numbers are all subscripts
An isolated event where bodies exert a relatively great amount of force to each other over a short period of time
external forces are not considered
Collision
Define elastic collision
The momenta and KEs of the bodies may change but the total momentum and total KEs are constant; typically have two unknowns
velocity is not changing; e.g. billiards, collision of particles, etc.
Pi = Pf ; KEi = KEf
T or F. The relative velocity of the two bodies has the same magnitude before and after the collision.
T
Final velocities in elastic collision, when one body is initially at rest
vA2 = (mA - mB / mA + mB) vA1
vB2 = (2mA / mA + mB) vA1
A’s, B’s, and numbers are all subscripts
define inelastic collision
only the total momentum is conserved; total KEs are not conserved (some KE are lost)
ΣKE ≠ constant ; Σp_i = Σp_f
Formula for KEi (initial energy)
KEi = KEf + lost energy
Initial energy was transformed to other forms (sound, thermal, etc.)
define perfectly inelastic collision
The collision is perfectly inelastic if the bodies stuck together after colliding.
Bodies have same final velocity.
p_1 = p_2
Define Center of Mass (CM)
mass-weighted average position of the particles; need not be within the object; behavior of motion of objects is similar to the motion of a particle
Unit: m (meters)
