1. Forces, Motion and Work

2. FORCE READ Unit 1 Lesson 3 page 28-39 text I
Force: simply a push or a pull
Unit is newton (N)
Can cause an object to change speed and direction (velocity)
doesn’t always cause an object to move
Types of forces:
Friction=contact force between two objects
Gravity= pulls us to Earth, acts at a distance
Magnetic Force= acts at a distance, push or pull

3. Causes of Friction
Adhesion is the molecular force resulting when two materials are brought into close contact with each other.
Surface roughness is a factor in friction when the materials are rough enough to cause serious abrasion (a.k.a. sandpaper effect)
When one or more of the materials is relatively soft, much of the resistance to movement is caused by deformations or a plowing effect.
Homework: Demonstrate or explain the 3 causes of friction.

4. Adhesion
Adhesion is the molecular force resulting when two materials are brought into close contact with each other.
Sticky materials like rubber and adhesive tape
Fluids: water droplets sliding down a window.
What will happen when you wet a coin on a ramp?

5. Surface Roughness
Surface roughness is a factor in friction when the materials are rough enough to cause serious abrasion.
What does each object look like up close?
If the surfaces of two hard solids are extremely rough, the "sandpaper effect" may occur.
particles of the materials are dislodged from their surfaces
At one time it was thought that the surface roughness of materials was the cause for friction. In reality, it only has a small effect on friction for most materials.

6. Plowing Effect
When one or more of the materials is relatively soft, much of the resistance to movement is caused by deformations or a plowing effect.
Soft materials will deform when under pressure. This also increases the resistance to motion.
Standing on a rug you sink slightly
Rubber tires deforming on road
When materials deform, you must "plow" through to move, thus creating a resistive force.

7. How can you increase frictional forces?
Decrease surface contact
Increase weight
Stop motion
Remove Lubrication

8. How can you increase frictional forces?
Decrease surface contact by making the surfaces rougher
Not a universal rule b/c two extremely smooth surfaces have increased electrostatic forces b/w them and actually will decrease frictional forces
Adding weight to one object can significantly increase the frictional force between two moving objects

9. Taking them out of motion.
Static friction is a different type of friction that indicates the amount of energy required to set an object in motion instead of the energy needed to keep it moving along, which relates to kinetic friction.
Static friction always requires more energy to start the object moving than it takes to keep it moving.
Remove a lubricant
Viscous solutions aid in the movement of objects (think oil for squeaking doors)
Homework: Demonstrate or explain the 4 ways to increase frictional force.

10. Newton’s Three Laws of Motion
An object at rest stay at rest, and an object in motion stays in motion at the same speed and direction, unless it experiences an unbalance force.
The acceleration of an object depends on the mass of the object and the amount of force applied.
Whenever one object exerts a force on a second object, the second object exerts and equal and opposite force on the first.

11. Gravity
Read pg U1L4
Gravity: is a force of attraction between objects due to their mass; a noncontact force
Pulls therefore is an attractive forces
9.8 m/s^2

12. Weight Earth’s gravity is felt by you as weight.
Weight is a force that depends on mass
The force of gravity between Earth and an object is equal to the mass of the object m multiplied by a factor due to gravity g
F=mg
g= 9.8 m/s^2
unit is the same as acceleration thus all objects accelerate toward Earth at the same rate!!!
Not a very powerful force

13. Gravity Gravity depends on… Distance
Gravitational force decreases as distance increases
(Insert diagram from pg. 46)
Mass
Gravitational force increases as mass increases

14. WORK
Unit 2 L1 Read pg
Work: the use of force to move an object some distance in the direction of the force
You do work when you exert a force on an object and move it
Only done by the part of the force that is in the same direction as the motion
Calculated by:
W=Fxd
Work= force x distance
Newton (force) x meter (distance)= newton-meter or joule (J) or work
1 joule of work completed when 1 newton of force moves an object 1 meter
Define work and how it is measured

15. WORK, Energy, and Power Energy Ability to cause a change or do work
When work is done, energy is transferred, and object must move for work to be done
Also expressed in joules
Power
The rate at which work is done or amount of energy transfer
2 machines lift the same weight or perform the same work, but the machine with more power does it quicker
Power= Energy/ t
P= E/t
joules/second or Watts (W)

16. MACHINEs Read Unit 2 Lesson 3 pages 102-113
Machine: any device that helps people do work by changing the way work is done; make tasks easier without decreasing the amount of work done
Simple machines: the machines that make up other machines
The six simple machines
Levers:
Wheels and axles
Pulleys
Inclined planes
Wedges
Screws

17. MACHINES
Remember: work is the use of force to move an object some distance
Input force: the force you apply to the machine through a distance
Work input: the work that you do on a machine
Work output: the work done by the machine on an object
Output force: the force a machine exerts on an object
Mechanical advantage
Mechanical advantage= output force/ input force
A machine that has a M.A.= 1, changes only the direction of the force
A machine that has a M.A.>1, produces greater output force
A machine that has a M.A.<1, requires greater input force, but the output force is applied through a longer distance
Mechanical efficiency: a comparison of the machine’s work output with the work input (M.E.= 9work output/ work input)x 100%

18. Simple machines
Lever: a bar that pivots at a fixed point called a fulcrum
3 classes based on position of fulcrum, load, and input force
1st class: fulcrum is between load and input force
2nd class: the load is between the fulcrum and the input force
3rd class: the input force is between the fulcrum and the load
Wheel and axle: made of a wheel connected to a smaller cylindrical object, axle
Ideal M.A.= radius input/ radius output

19. Simple machines
Pulley: has a grooved wheel that holds a rope or a cable
3 types
Fixed pulleys: attached to something that does not move
Moveable pulleys: attached to an object being moved
Block and tackle pulleys: combining a fixed and movable pulley
Inclined plane: a straight, slanted surface
Ideal mechanical advantage= length/ height
Wedges: a pair of inclined planes that move; have one thick and one thin end
Screws: an inclined plane wrapped in a spiral around a cylinder

20. PROJECT Rube Goldberg Challenge Define a task
Create a machine using at least 3 simple machines to complete the defined task
Write at least a one page, double-spaced, 12 point font essay on the simple machines in your machine and Newton’s 3 laws