Mechanics 3 - Types of forces Flashcards
What is centre of mass
- Point where the all the mass of the object (irregular) is concentrated i.e point where weight mg acts
How to find a centre of mass?
Hang an object and the rotational forces on either side pf the COM cancels out, leaving the mass to run through the centre of mass.
If you place a finger at COM and provide support force, it will balance
What rotates a ball in the air?
The rotation of a ball in air is relative to its COM
Friction force
Force between surfaces and it is parallel to the surfaces
*It always opposes relative motion
What is f (max)
The force required to move a stationary object, once you move it less force is needed.
f(max) = coeff x Normal force
f isn’t proportional to weight force as you can add more weight force but Normal responds to changes in weight force. This is because N = w and N = mg
What should the values of (coeff in micro-) be?
Coeff should be < (close to one) in scenarios of friction on road, need friction to keep car on the road
Coeff should be «_space;(very small) as in animals joints, we need least amount of friction for mobility (friction also generates heat, which is bad)
Atmospheric pressure
- Objects in air experience drag and have to push particles away, resulting in friction that opposes motion
- More SA and speed means more resistance because there is more interaction with particles.
How is terminal velocity reached?
When an object is dropped, it first accelerates downwards due to gravity. Upward force is exerted due to air resistance. The big net force difference slowly decreases until it becomes balanced i.e net force = 0 and terminal velocity is reached.
Why do heavier objects fall down faster?
Because they need more air resistance to reach terminal velocity. Hence, it will fall faster for more interaction with particles to reach terminal velocity.
Law of lever
At balance, its at equilibrium
*The fulcrum allows rotation, but at balance the rotational forces cancel out.
- Fd is the torque i.e measure of the rotating forces i.e tendency to rotate
F1d1 = F2d2 –> effort x effort arm = load x load arm