Download presentation

Presentation is loading. Please wait.

1
**Resistance in Mechanical Systems**

Unit 4 – Subunit 1

2
**When an object rests on a floor, the weight of the object is a force that pushes down on the floor.**

At the same time, the floor pushes back up on the object to counter the objects force. The object is in vertical equilibrium

3
**Vertical Equilibrium Equilibrium is when two forces are in balance.**

Vertical equilibrium is when the weight of an object is countered by an opposing force.

4
The force that pushes back (or up) is called the Normal Force (N) because it is perpendicular to the surfaces of contact. Examples of normal forces are: floor hand lift thrust

5
**Can an object in equilibrium be moving? **

Remember When an object rests on a floor, the weight of the object is a force that pushes down on the floor. At the same time, the floor pushes back up on the object to counter its force. The object is in vertical equilibrium Question: Can an object in equilibrium be moving? Yes – think of being in an elevator. It also can be moving horizontally > > > > >

6
Friction Friction is a force that opposes the force that causes motion. Friction is caused by the roughness of a surface

7
**The two types of friction are :**

Static – stationary friction this is the initial friction on a non moving object with a force applied. Kinetic – moving friction This is the friction that is generated as the object moves.

8
**The amount of friction depends upon:**

Nature of the surfaces in contact Force that presses the two surfaces together Friction does not depend upon: The rate at which the objects are moving (unless its stationary vs moving) Size of the contact area

9
**The Coefficient of Sliding Friction**

MEW tomorrow

10
**The amount of friction depends upon:**

Remember: The amount of friction depends upon: Nature of the surfaces in contact Force that presses the two surfaces together The ratio of the frictional force to the normal force is called the “Coefficient of Friction”

11
μ Coefficient of Friction “μ“ Pronounced Mew & spelled mu μ represents the measure of the frictional characteristic between the surfaces of materials The higher the value of μ, the more frictional force is present when sliding occurs (or movement)

12
**The formula for the coefficient of friction:**

μ = f / N Where f = the frictional force generated N = the Normal force (= to weight)

13
**(in order of increasing resistance)**

The three μ’s (in order of increasing resistance) μs = coefficient of static friction μk = coefficient of kinetic friction μr = coefficient of rolling friction

14
**See example 4-A and 4-B on page 11**

Complete problems 1,2 and 6,7,8 on pages 22 & 23. These problems deal with mechanical resistance. Tomorrow: Effects of lubricants Rolling friction Drag in fluid systems

15
**Lubricants in Mechanical Systems**

Lubricants protect sliding surfaces by providing a thin layer of fluid between them. The lubricant between two surfaces does three things: Reduces friction Reduces wear Reduces heat

16
Drag Drag is a mechanical resistance produced when an object moves through a fluid. A fluid can be either a liquid or a gas

17
**The formula for Drag Resistance is: Rd = F/v Where:**

Rd = drag resistance F = drag force V = speed (velocity)

18
Assuming constant velocity, an airplane will be in both horizontal and vertical equilibrium as it moves through the air

19
Streamlining Streamlining reduces Drag Streamlining reduces turbulence

20
**Complete problems 2, 3,4, 8 & 9 - pg 22/23**

Complete “lets Review” on top of page 22 (units) Complete “Student Exercises” on page 17

Similar presentations

Presentation is loading. Please wait....

OK

FORCES Mrs. Cholak.

FORCES Mrs. Cholak.

© 2018 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on consumer equilibrium in case of two commodity Ppt on standing order act 1946 ford Ppt on contact and noncontact forces Ppt on albert einstein biography Ppt on basic proportionality theorem for class 10 Ppt on articles of association form Ppt on personal swot analysis Download ppt on my role model Ppt on limitation act malaysia Ppt on coalition government in uk