Forces, Motion and Work

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

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. 42- 45 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 • (Insert diagram from pg. 46)

14. WORK • Unit 2 L1 Read pg. 78-85 • 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

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