| A | B |
|---|
| Work. | is done when a force exerted on an object causes that object to move some distance; equal to force times distance;measured in joules ( J ). |
| Power. | rate at which work is done; equal to the work done divided by the time it takes to do the work; measured in watts. |
| Input force. | force exerted on a machine. |
| Output force. | force exerted by a machine. |
| Mechanical advantage. | number of times the input force is multiplied by a machine; equal to the output force divided by the input force. |
| Efficiency. | equal to the output work divided by the input work; expressed as a percentage. |
| Simple machine. | a machine that does work with only one movement; includes the inclined plane, wedge, screw, lever, wheel and axle, and pulley. |
| Compound machine. | machine made up of a combination of two or more simple machines. |
| Inclined plane. | simple machine that is a flat surface, sloped surface, or ramp. |
| Wedge. | simple machine consisting of an inclined plane that moves; can have one or two sloping sides. |
| Screw. | simple machine that is an inclined plane wrapped around a cylinder or post. |
| Lever. | simple machine consisting of a rigid rod or plank that pivots or rotates about a fixed point called the fulcrum. |
| Wheel and axle. | simple machine made from two circular objects of different sizes that are attached and rotate together. |
| Pulley | simple machine made from a grooved wheel with a rope or cable wrapped around the groove. |
| What is a requirement in order for work to be done? | force moves an object |
| How much work is done when a force of 60N moves an object a distance of 3 m? | 180 J |
| How much power is used when 300 J of work are done in 10 s? | 30 W |
| Give some examples of simple machines. | baseball bat, scissors, wheel barrow |
| What is the ideal mechanical advantage of a machine that changes only the direction of the input force? | 1 |
| What is the output force if the input force on a wheel is 100 N? (the wheel has a radius of 3 cm and an axle has a 1 cm radius) | 300 N --- WHY--- (Page 594 - Mechanical Advantage = radius of the wheel divided by the radius of the axle - 3/1 = 3) (Page 587 - Output force divided by Input force = Mechanical Advantage - What divided by 100 = 3? Answer = 300 N) |
| Name several inclined planes. | Ramps, wedges, and screws |
| For a given input force, a ramp increases ... | output force. |
| Would a 9 N force applied 2 m from the fulcrom on a lever lift a 9 N force applied 3 m from the fulcrum on the opposite side of the lever? | No, the 9 N force would have to be applied at least 3 m from the fulcrum. |
| Explain why the output work for any machine can't be greater than the input work. | When work is done ON the machine, energy is transferred to the machine. When work is done BY the machine, the machine transfers energy to another object. According to the law of conservation of energy, energy cannot be created or destroyed. |
| A door knob is an example of a wheel and axle. Explain why turning the knob is easier than turning the axle. | The radius of the knob is greater than the radius of the axle. This means that when a force is applied to the knob, the knob moves a greater distance than the axle. The knob and the axle do the same amount of work. Therefore, the axle must multiply the force. |
| On the Moon, the force of gravity is less than on Earth. Infer how the mechanical advantage of an inclined plane would change if it were on the Moon, instead of on Earth. | The mechanical advantage of an inclined plane would be the same on Earth as on the Moon. The mechanical advantage of an inclined plane depends only on its length and height. |
| Changing Distance.Figure 5. | some machines allow you to exert your force over the shorter distance.Changing the direction or the distance that a force is applied can make a task easier. |
| Friction. | force that opposes motion between two touching surfaces. |
| Compound. | made of separate pieces or parts. |
