Mechanical Systems

Question 1

What are the 2 most common factors that influence friction?

Answer 1

Roughness or smoothness

The normal force

Question 2

What is the coefficient of friction?

Answer 2

Greek u

Magnitude of the force of friction over the magnitude of normal force

Question 3

What is the coefficient of kinetic friction and when is it used?

Answer 3

Magnitude of kinetic friction / magnitude of normal force

Used when the object is already moving at a constant velocity

Question 4

What is the coefficient of static friction

Answer 4

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

Question 5

What is the normal force assuming gravity always points down and the normal force always points up?

Answer 5

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

Question 6

What are some ways of decreasing friction?

Answer 6

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

Question 7

What are ways of increasing friction in tires?

Answer 7

Maintaining proper inflation to ensure maximum surface area stays in contact with the road
Good treads remove water and prevent hydroplaning

Question 8

What are the 5 functions of machines?

Answer 8

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

Question 9

What are the 3 classes of Levers?

Answer 9

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)

Question 10

What are other objects in the lever family not included in the 3 classes?

Answer 10

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

Question 11

What is an inclined plane and the 2 types

Answer 11

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

Question 12

What is a compound machine?

Answer 12

A compound machine is a machine made of two or more simpler machines.

Question 13

How do you calculate torque?

Answer 13

T=F*d
T = Torque in Newton metres (Nm)
F = Force in Newtons (N)
d = Distance to the pivot point in metres (m)

Question 14

What are the 2 types of Torque on a lever

Answer 14

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))

Question 15

What is the Law of the Lever?

Answer 15

For any lever is static equilibrium:
Effort torque = Load torque
F (effort) * d (effort) = F (load) * d (load)

Question 16

How is mechanical advantage (MA) calculated for a lever in static equilibrium?

Answer 16

MA = F (load) / F (effort)\
If MA>1, there is a mechanical advantage (F (load) > F (effort)
If MA<1, F(load) < F (effort)

Question 17

How is Ideal Mechanical Advantage (IMA) calculated for a lever in static equilibrium?

Answer 17

IMA = d (effort) / d (load)

IMA > 1, effort arm > load arm

Question 18

How is IMA calculated for other machines?

Answer 18

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

Question 19

How is work defined and calculated in physics?

Answer 19

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

Question 20

Explain the situations in which zero work is done

Answer 20

If the object has zero displacement
If force = 0 acting on the object
If the force exerted is perpendicular to the displacement

Question 21

What is negative work and how is it calculated?

Answer 21

Negtive work is when a force acts in the direction opposite of the displacement
W = -F∆d

Question 22

How do you calculate work done using a force-displacement graph

Answer 22

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

Question 23

How do you calculate work done by friction

Answer 23

Use formula for negative work (W=-F∆d)

Friction acts against active force

Question 24

How do you calculate work done to lift objects at a constant velocity?

Answer 24

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

Question 25

What are input and output work and how are they calculated?

Answer 25

Input Work: the work done to make the task happen

Output Work: the total work done (sum of input work and negative work, value is less than Input work)