Mechanical Systems Flashcards
What are the 2 most common factors that influence friction?
Roughness or smoothness
The normal force
What is the coefficient of friction?
Greek u
Magnitude of the force of friction over the magnitude of normal force
What is the coefficient of kinetic friction and when is it used?
Magnitude of kinetic friction / magnitude of normal force
Used when the object is already moving at a constant velocity
What is the coefficient of static friction
Magnitude of static friction over the magnitude of normal force
Used when an object is not yet moving and some applied force acts on it
What is the normal force assuming gravity always points down and the normal force always points up?
F of N = m (mass) * g (gravity, 9.8m/s^2)
This is only true when the object is on the ground, the normal force must even out the force of gravity
What are some ways of decreasing friction?
A lubricant can be used such as oil (eventually breaks down and must be replaced)
Insert mechanical joints called bearings (can wear out)
Shape and smoothness can reduce friction with air and water
What are ways of increasing friction in tires?
Maintaining proper inflation to ensure maximum surface area stays in contact with the road
Good treads remove water and prevent hydroplaning
What are the 5 functions of machines?
Change the magnitude of a force Change the direction of a force Transfer force from one place to another Change speed or distance Change energy from one form to another
What are the 3 classes of Levers?
Class 1: the pivot is between the effort force and the load force (using a stick to move a rock)
Class 2: the load force is between the effort force and the pivot (can crusher)
Class 3: the effort force is between the load force and the pivot (forearm movement)
What are other objects in the lever family not included in the 3 classes?
Pulley: pivot in the middle, load on one side and effort force on the other
Wheel and Axle: wheel is turned by effort force, pivot is in the middle connecting the wheel and axle, load force on the axle
Gears
What is an inclined plane and the 2 types
An inclined plane is a ramp which allows for a lower effort force to be exerted
Wedge: inclined plane on both sides to separate two objects or one object into 2 pieces
Screw: thread is an inclined plane in a circular pattern
What is a compound machine?
A compound machine is a machine made of two or more simpler machines.
How do you calculate torque?
T=F*d
T = Torque in Newton metres (Nm)
F = Force in Newtons (N)
d = Distance to the pivot point in metres (m)
What are the 2 types of Torque on a lever
Effort torque (use force (N) * distance to the pivot point (m) to calculate torque (Nm)) Load Torque (use force (N, sometimes related to gravity force (m*g)) * distance to the pivot point (m) to find torque (Nm))
What is the Law of the Lever?
For any lever is static equilibrium:
Effort torque = Load torque
F (effort) * d (effort) = F (load) * d (load)
How is mechanical advantage (MA) calculated for a lever in static equilibrium?
MA = F (load) / F (effort)\
If MA>1, there is a mechanical advantage (F (load) > F (effort)
If MA<1, F(load) < F (effort)
How is Ideal Mechanical Advantage (IMA) calculated for a lever in static equilibrium?
IMA = d (effort) / d (load)
IMA > 1, effort arm > load arm
How is IMA calculated for other machines?
Pulley: IMA = amount of tension points
Wheel and axle: same as lever but effort arm = effort radius and load arm = load radius
Inclined plane: IMA = length of incline/height
Set of gears: IMA = # teeth in effort gear/ # of teeth in load gear
How is work defined and calculated in physics?
Work: when a force acts on an object and the object moves through a displacement W = F∆d W is work done in joules (J) F is force in N ∆d is magnitude of displacement
Explain the situations in which zero work is done
If the object has zero displacement
If force = 0 acting on the object
If the force exerted is perpendicular to the displacement
What is negative work and how is it calculated?
Negtive work is when a force acts in the direction opposite of the displacement
W = -F∆d
How do you calculate work done using a force-displacement graph
If force is constant, use W = F∆d
If force is not constant, find the area (note: area of a triangle is 1/2b*h
How do you calculate work done by friction
Use formula for negative work (W=-F∆d)
Friction acts against active force
How do you calculate work done to lift objects at a constant velocity?
Newtons first law, Net force = 0 when objects move at a constant velocity
Active force = force of gravity
W = F∆d where F = force of gravity
