Newtons Laws & Momentum Flashcards
Newton’s first law
An object will remain at rest or a constant velocity unless acted upon by an external force
Newton’s second law
The resultant force acting on an object is directly proportional to the rate of change of momentum
F = △ p / △ t
F △ t = mv - mu
Newton’s third law
When 2 objects interact, they will exert equal and opposite forces
- They must both act on different objects
- They must be equal and opposite is magnitude
- The forces are of the same type/nature (you can reverse the order of x and y and it still makes sense)
Example of Newton’s third law
A skydiver - the air particles are pushing against the man and the man is pushing against the air particles at an equal force
What is an impulse?
The average net force acting on an object multiplied by the time it acts on it
Impulse = Force x Time
Impulse = Change in momentum
Impulse = mv - mu
What is the area under a F against T graph?
The impulse
What is the principe of conservation of momentum?
The total momentum in a system remains unchanged unless there is an external force acting on in
Total initial momentum = Total output momentum
What is linear momentum?
When objects are moving and/or interacting in one dimension
What is a perfectly elastic collision? - Give an example
A collision where momentum and kinetic energy is conserved
E.g - molecular motion
What is a perfectly inelastic collision? - Give an example
A collision where momentum is conserved but kinetic energy is NOT
E.g - billard balls
(Objects may stick together after colliding)
If object A collides into object B, how do you calculate the velocity of object B after a collision?
Momentum in the positive direction of A = Momentum in the negative direction of A and B
(A- Mass x initialV) = -(A- Mass x finalV) +(B- Mass x Xvelocity)
[rearrange for Xvelocity]
Xvelocity = (A- Mass x initialV) + (A- Mass x finalV)/ (B- Mass)
If object A collides into object B, and continue moving in the same direction together, how do you calculate their velocity afterwards ?
Momentum before = Momentum after
(A- Mass x initialV) + (B- Mass x initialV - if stationary=0) = (Combined mass of AB x Xvelocity)
[rearrange for Xvelocity]
Xvelocity = + (A- Mass x initialV) + (B- Mass x initialV)/Combined mass of AB
Explain why kinetic energy is not conserved in an inelastic collision
Some of the KE is transferred into other forms and therefore does not remain equal to the initial energy
Principles of collisions in 2 dimensions
Where objects move off at different angles after colliding
- Conservation of momentum applies in all directions
- Momentum and/or velocity can be resolved into 2 perpendicular components to solve problems
Equation for momentum of collisions in 2 dimensions
P1y = P2x
P1 and P2 —> perpendicular direction to motion
y —> 90° - beta0
(90° - angle of rebound from the normal - initial horizontal motion)
Define drag and the factors that affect it
A frictional force that opposes motion through a fluid
Factors:
- Cross-sectional area
- Speed
- Viscosity of fluid
Determining the terminal velocity PAG
- Take a measuring cylinder and fill it with a viscous liquid.
- Hold a ball bearing over the surface of the liquid and release it from rest. (you may use a magnet.)
- Start a timer and mark the position of the ball bearing within the tube through time intervals.
- You will know when the ball reaches terminal velocity when the distance between each time interval is the same/becomes a pattern.
- (To increase accuracy video the experiment and place the cylinder against a tape measure so you can replay and mark the intervals accurately.)
