3.5 - Newton's Laws and Momentum Flashcards
What is Newton’s first law of motion?
An object will remain at rest or continue to move with constant velocity unless acted on by a resultant force
What is Newton’s second law of motion?
The resultant force acting on an object os directly proportional to the rate of change of momentum, and is in the same direction
What is Newton’s third law of motion?
When 2 objects interact they exert equal and opposite forces on each other
When 2 objects interact a pair of forces is produced, which will always be equal and opposite. These forces acting on the interacting objects are always of the same type.
What are the different types of interactions?
Four fundamental forces:
- gravitational
- electromagnetic - eg when you push hands together, force is due to repulsion between electron clouds and atomic nuclei in your hands
- strong nuclear
- weak nuclear
Both nuclear forces are very weak and have little impact on our daily lives
What is linear momentum?
- a vector quantity
- product of an objects mass and its velocity
- units kgm/s
What is the equation for momentum?
p = mv
p= momentum, kgm/s
m=mass, kg
v=velocity, m/s
What is the principle of conservation of momentum?
For a system of interacting objects, the total momentum in a specified direction remains constant as long as no external forces act on the system
State and explain the total momentum of a gun
total momentum = 0 (as before momentum = 0)
- the gun recoils when the bullet is fired
- the magnitude of momentum for the gun and the bullet is the same, but they are acting in opposite directions so momentum = 0
- same is true for an exploding firework, shooting a cannon, recoiling radioactive nucleus when it emits an alpha particle
Describe a perfectly elastic collision
Momentum = conserved
Total energy = conserved
Total kinetic every = conserved
Describe an inelastic collision
Momentum = conserved
Total energy = conserved
Total kinetic energy = not conserved
What is the equation for newtons 2nd law?
F = Δp/Δt
F = force, N Δp = change in momentum, kgm/s Δt = change in time, s
How is then equation for Newton’s second law derived?
Newton’s second law states that net force ∝ rate of change of momentum.
1) F ∝ Δp/Δt
2) this can be written as F = kΔp/Δt, where k is a constant
3) k can be made to equal 1 by defining the unit of force asthe force required to accelerate a 1kg mass by 1 m/s²
F = Δp/Δt
What is a special equation for Newton’s 2nd law?
F = ma
1) F = Δp/Δt
2) Δp = m x Δv = m(v-u)
Sub in: F= m(v-u)/t
3) (v-u)/t = acceleration
F = ma
This is a special case that only works when mass is constant
Why is momentum conserved?
According to newtons 3rd law, if 2 objects interact, they both experience an equal and opposite force
This means net force = 0
According to Newton’s 2nd law, F= Δp/Δt = 0, so Δp must equal 0
This means momentum is conserved
What is impulse?
- a change in momentum
- this is a result of an object in a collision experiencing a force for a certain amount of time
- measured in Ns or kgm/s
