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# Forces, work and machines

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review of forces unit using a concept map, followed by very brief introduction to the topic

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### Forces, work and machines

1. 1. Forces, work and machines
2. 2. Goals for today• Overview of the topic• Review forces• What is work?• What are the simple machines?• Define compound machines• Describe a Rube Goldberg device
3. 3. Newtons Forces A push, a pull or a twist A in a particular directionCan beshown direction magnitudeas a An arrow 4N Balanced Unbalanced
4. 4. Is a push or a pull (or a twist)• Forces can be: – Contact • Friction – Non-contact • Gravity (weight) • Magnetism• Forces change the speed, direction or shape of an object.
5. 5. Newtons• After Sir Isaac Newton
6. 6. • Buoyancy• Electrostatic• Air resistance• Gravity• Electricity
7. 7. Vector• A vector is a line with an arrow. It begins with a dot Each square = 1newton• It shows both the direction and the magnitude of the force
8. 8. Net force• When more than one force acts on an object, the forces combine to form a NET FORCE.• Forces may work together or they may be opposite forces
9. 9. Net force = 0• Two or more opposite forces are BALANCED if their effects cancel each other and they do not cause a change in the objects motion 100N 100N
10. 10. Net force 0• If the effects of the forces dont cancel each other, if one force is stronger than others, the forces are unbalanced forces.• Unbalanced forces cause a change in motion; speed and/or direction.
11. 11. • When two forces act in the same direction on an object, the net force = sum of the two forces.
12. 12. • When two unequal forces act in opposite directions on an object, the net force is the difference of the two forces
13. 13. What is work?• Work happens when a force moves an object• Work is the energy needed to move something over a certain distance. It is measured in Joules (J) Measured in metres (m) Measured in Newtons (N)
14. 14. • Let’s say that a certain job takes 12 joules to do it. We could do that job in a number of different ways.
15. 15. • What this all means is IF THE DISTANCE WE MOVE IS GREATER, THE EFFORT WE NEED TO PUT IN IS LESS
16. 16. Simple Machines• Machines make work easier• Machines change the size, distance or direction of a force
17. 17. Compound machine• A compound machine is a machine with two or more simple machines working together to make work easier• A bicycle is a compound machine – it uses wheels, levers and gears to help a person travel a greater distance with less effort
18. 18. screw Wheel and axle wedgewedge lever lever
19. 19. Rube Goldberg• A famous cartoonist• Known for his comical drawings of crazy contraptions and inventions that made simple tasks into difficult and complicated ones
20. 20. Possible Materials• Possible Materials: string, candle, mousetrap, paper tube, spools, marbles, Legos, dominoes, tinker-toys, Barbie dolls, hot wheels, weights (sinkers), golf balls, Ping-Pong balls