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1

Mechanical System

A group of physical parts that interact with each other to complete a task.

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2

Gravity

The attraction between two objects due to their mass, dependent on the amount of mass and distance between the objects.

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3

Force

A push or pull that acts on an object.

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4

Contact Forces

Forces that require physical contact with the object they push or pull, such as hitting a tennis ball.

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5

Inertia

The tendency of an object to resist changes in its motion.

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6

Friction

A force that opposes the relative motion of an object.

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7

Action-at-a-distance

Forces that can push or pull an object without physical contact, such as gravity, static electricity, and magnetism.

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8

Mass

The amount of matter in an object.

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9

Weight/Force of Gravity

The amount of force on an object due to gravity.

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10

Newton

The metric unit for force, measuring the force of gravity.

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11

Spring Scale

A scale consisting of a spring with a hook, where the more force applied, the farther the spring stretches.

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12

Calculating the force of gravity

The weight of an object on Earth is calculated by multiplying its mass by 9.8 N/kg, symbolized by g.

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13

Work

The amount of effort spent when a force causes an object to move a distance.

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14

Energy

The ability to do work, measured in joules.

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15

Kinetic Energy

The energy an object has when it is moving.

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16

Potential Energy

Energy that is stored.

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17

Gravitational Potential Energy

The potential energy of an object that is able to fall.

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18

Work Formula

Work is calculated by multiplying the newtons by the distance moved in meters.

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19

Since energy cannot be lost, where does it go?

It converts from one form of energy to another.

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20

Machine

Any mechanical system that reduces the force required to accomplish work.

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21

Three ways machines make work easier

Increasing the force, increasing the distance, or changing the direction of the force.

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Examples of machines

Nutracker: A machine that increases the force applied to an object by reducing the distance over which the force is applied.

Ramp: Machine that increases the distance over which the force is applied to an object by reducing the force required to move it.

Stairs: Machines that change the direction of the force applied to move from one level to another.

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23

Input and output forces

Two forces are always involved when a machine is used to do work, an input force, and an output force. The input force is the force that is applied to the machine, and the output force is the force that the machine applies to the object.

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24

Mechanical Advantage Formula

The formula for mechanical advantage is: MA = output force in newtons / input force in newtons

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25

Mechanical Advantage

The amount by which a machine can multiply an input force. Machines such as nutcrackers, ramps, and car jacks all have mechanical advantages, because the output force is greater than the input force.

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Ways machine can change a force

Machines can increase the distance over which the force is applied, multiply the input force, and change the direction of the force.

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27

Mechanical advantage of 1

Machines like fixed pulleys have mechanical advantage of 1, because the input and output force remain the same size, and only the direction of the force is being changed. If the only way a machine changes a force is its direction, the mechanical advantage is 1.

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28

Ideal mechanical advantage (IMA)

In real machines, some work done by the input force is made into thermal energy by friction in the machine, and so, the work done by the output force is less than the work done by the input force. An ideal machine has no friction, therefore no energy is converted to thermal energy. The mechanical advantage of a machine that has no friction is called the ideal mechanical advantage.

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Equation for Ideal Mechanical Advantage.

IMA = input distance / output distance.

Example: Padma uses a hammer to pull a nail. If she moves the handle of the hammer 30 cm and the nail moves 5.0 cm, the IMA would be (30 cm) / (5.0cm), which means the IMA would be 6.

Although no real machines have zero friction, some machines have very little friction, like hammers and screwdriveres.

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30

IMA of less than 1

Sometimes, the IMA is under 1 and the output distance is greater than the input. This means that the speed at the output is higher than the input. Examples of these machines with less than 1 IMA are hockey sticks, baseball bats, and garden rakes. In each of these, the distance moved by the input force is less than the output force.

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