Mechanics 3 - Newton's Laws, Terminal Velocity, Momentum Flashcards
What is Newton’s 1st Law of Motion?
If no resultant force acts on a body, then it will either remain at rest, or continue moving with constant velocity (no acceleration)
What is Newton’s 2nd Law of Motion?
The rate of change of momentum (acceleration) of a body is directly proportional to the resultant force acting on it
Fres ∝ a
What is Newton’s 3rd Law of Motion?
When two objects interact, they exert an equal and opposite force on each other and the forces are of the same type
If the forces acting on an object are balanced what can you say about its motion?
There is no resultant force so it will continue moving at a constant velocity. It won’t accelerate.
What’s wrong with this?
In F=ma, F must be the resultant force!!!
How does an object reach terminal velocity?
As it speeds up, air resistance increases, decreasing the resultant force.
Eventually air resistance = driving force, Fres=0 so a=0.
What two things are the case for tension?
- Tension always acts away from the contact points
- Tension is constant throughout the rope/wire/ cable
Why are objects never truly in freefall?
There will always be air resistance opposing the weight
(Apart from when v=0)
What is the condition for terminal velocity?
The drag force = driving force (or weight) so Fres=0 and so a=0
What factors affect the drag force on an object?
- Fluid density
- Shape of object
- Cross sectional area of object
- Velocity of object
Why does air resistance increase with velocity?
The object is colliding with more air molecules per second
What does the velocity time graph of an object reaching terminal velocity look like?
What’s wrong with this?
The acceleration is not constant so you cannot use SUVATs
Instead use area under graph
How is momentum calculated?
What’s wrong with this?
Direction must be taken into account (as momentum is a vector)