Introduction to Physics and Simple Machines

Introduction to Physics and Simple Machines Machine •  Any tool that helps to do work. •  Machines do not change the amount of work done. http:// ...
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Introduction to Physics and Simple Machines

Machine •  Any tool that helps to do work. •  Machines do not change the amount of work done.

http:// www.youtube.com/ watch? v=hSI5HjHOiiY&featur e=related

Is the transfer of energy through motion.

If I push a wall for 1 hour and the wall does not move

• Has Work been done on the wall?

• Why or Why not?

•  Work is done on an object when a force causes the object to move some distance. – No work without motion – No work without force in the same direction as the motion. – Work requires a net force.

Calculating work •  Work = Force X Distance – Force units = Newton, N – Distance units = meter, m – Work units = Joule, J or Newtonmeter (1 N is the force required to move 1 kg 1 m/s2 or 100 g 10 m/s2)

Motion and force •  Person does no work on weights if weights do not move Force on weights

•  Person does work on weights when weights move Force on weights

One Joule •  Is the amount of work required to exert a force of one Newton for a distance of one meter

Machines can help do work in 3 ways: •  1. Can increase the force applied to an object. •  2. Can change the direction of the force. •  3. Can increase the distance through which a force moves.

The amount of effort saved when using simple or complex machines is called mechanical advantage or MA.

Mechanical advantage (MA)

• Mechanical advantage is the number of times a machine increases an effort force. •  M.A. = resistance force effort force

•  Force applied to the machine is called Effort Force (Fe) •  Resistance Force (Fr) is the force produced by the machine (applied by the machine on the object).

•  Any M.A. number higher than one requires less effort •  If M.A. > 1 required effort is reduced but effort distance increases •  If M.A. < 1 required effort is increased but effort distance is decreased

The more force applied, the more work the machine will do.

Ideal Machine •  A machine in which the work input equals the work output (This is not actually possible). We will be using IMA (Ideal Mechanical Advantage) for our work.

Simple Machine Simple machines are types of machines that do work with one movement.

Compound Machines Made by combining two or more simple machines Examples: Bikes, Can openers

A wheelbarrow is an example of a complex machine (compound machine) that uses a lever and a wheel and axle.

6 types of simple machines

• Lever • Pulley • Wheel and Axle

• Inclined plane • Screw • Wedge

•  Slanted surface used to raise an object •  MA = length of the plane height

Work done will be the same whether straight up or inclined plane •  Remember: Work = force X distance. When lifting straight up the distance is small but more effort. Using a plane, the distance is longer but force is less.

In its simplest form, a lever is a stick that is free to pivot or move back and forth at a fixed point (fulcrum). The easiest way to remember the difference is the order of the Effort (E), Resistance (R), and Fulcrum (F).

•  Effort Force (Fe): The force exerted on a lever. •  Fulcrum: A support or pivot point in a machine. •  Resistance Force (Fr): The force a lever exerts on the resisting object.

3 classes of Levers Always depends on position of fulcrum to the effort arm and resistance arm.

First class lever • The fulcrum is between the effort force and resistance force

Second class lever The resistance is between the effort and the fulcrum example : nut cracker

Third Class The effort is between the fulcrum and the resistance example: throwing a baseball

Mechanical Advantage for a Lever • MA = effort arm length resistance length

Pulley  Changes the direction or location of the effort force or may reduce the effort force necessary to move an object

MA for a pulley •  Number of supporting strings or •  Total number of ropes - 1 MA = 1

MA = 2

A single fixed pulley only changes the direction of the force. The M.A. is 1. The M.A. of a single movable pulley is 2.

A wheel and axle is a lever that rotates in a circle around a center point or fulcrum. The larger wheel (or outside) rotates around the smaller wheel (axle).

• Bicycle wheels and gears are examples of a wheel and axle. Wheels can also have a solid shaft with the center core as the axle such as a screwdriver or drill bit or the log in a log rolling contest.

Wheel and Axle M.A. •  Ratio of the radius of wheel to the radius of axle gives the mechanical advantage

MA for wheel and axle Radius of the wheel Radius of the axle

The radius of the wheel will be larger because we always wants the MA to be greater than 1.

•  A wedge is an inclined plane which moves. Most wedges (but not all) are combinations of two inclined planes. A knife, axe, razor blade, and teeth are all good examples of wedges.

Generally it can be anything that splits, cuts, or divides another object including air and water. MA = Length Height

• A screw, like a wedge, is another form of an inclined plane. A screw is an inclined plane wrapped around a cylinder to form a spiral.

Screw M.A. = more threads = higher M.A. fewer threads = lower M.A.

End Simple Machines

Introduction to Physics Terms

Speed •  Speed is the distance traveled by an object in a unit of time, that is, speed is the rate of change of the position of the object. Speed = Distance Time Ft/sec. or m.p.h. (miles/hour)

Velocity •  Velocity indicates the speed and direction of travel. Example: 55 m.p.h. North

Acceleration •  Changes in velocity are called acceleration. (A decrease in velocity is deceleration.) •  Acceleration is the change in velocity divided by the time it takes to make this change. •  Gravity (g) = 9.8 m/s2 2 = 32 ft/sec

Force • Push or pull that starts, stops, or changes the direction of an object

Forces

• Balanced • Unbalanced

Balanced • Forces are equal and opposite in size

• Balanced forces do not cause motion

Unbalanced forces • Are not opposite and not equal

• Unbalanced forces will cause motion

Example

• If a sliding book comes to rest then a force (s) must have opposed its motion. What force(s) are working against the motion of the book?

Objects

Gravity •  Is a force that every object exerts on every other object. The amount of gravitational force is dependent on the mass of the object and the distance between them.

Friction •  Is the force that opposes motion between two surfaces that are touching each other.

Net Force • Unbalanced forces result in a net force. A net force on an object always changes the velocity of the object.

Centripetal forces Centripetal is Latin for "center seeking".

Bolas

Centripetal force means that the force is always directed toward the center of the circle. Without this force, an object will simply continue moving in straight line motion which is often confused with centrifugal force.

Centrifugal forces are referred to as center fleeing

This is the force that helps to remove water from your clothes in your clothes washer. There is debate as to whether this is a force or lack of centripetal force resulting in inertia.

Section 2

Bernoulli s Principle •  States that as the velocity of a fluid increases the pressure exerted by the fluid decreases.

•  The curve of an airfoil's upper surface makes the air flowing over it move faster than the air flowing under the wing. This increase in velocity reduces the pressure on the top of the wing so lift is produced. Lift is also called airfoil lift or Bernoulli's lift.

Curve Ball

Is the transfer of energy through motion.

Calculating work •  Work = Force X Distance – Force units = Newton, N – Distance units = meter, m – Work units = Joule, J or Newtonmeter (1 N is the force required to move 1 kg 1 m/s2 or 100 g 10 m/s2)

One Joule •  Is the amount of work required to exert a force of one Newton for a distance of one meter

• Rate at which work is done.

• Power = work time

One horsepower equals 746 watts

Power is measured in Watts

• One watt = one joule per second • Watt was named by James Watt

Most power is measured in Kilowatts • One kilowatt = 1000 watts

End of Physics Terms

Newton’s Laws of Motion

Newton in 1665 Three Laws of Motion

•  Motion is a change in position relative to a body assumed to be not moving.

The Laws explain… Rest, constant motion and accelerated motion, as well as how balanced and unbalanced forces act to cause motion.

•  Have you ever been riding in a car when the driver suddenly slammed on the brakes? How did your body move as the car came to a stop?

1st law of Motion The law states that a body at rest tends to remain at rest, and a body in motion tends to remain in motion in a straight line unless the body is acted upon by an unbalanced force.

•  Momentum is the wanting to continue forward motion acquired by a moving body as a result of its motion.

Newton called his first law inertia. Inertia is the tendency to remain in motion or stay at rest

•  The force of an object is equal to its mass times its acceleration.

2nd Law of motion An unbalanced force accelerates the object in the direction of that force

A speeding bullet and a slow moving train both have tremendous force. The force of the bullet can be attributed to its incredible acceleration while the force of the train comes from its great mass.

Force = Mass x Acceleration • Force is measured in newtons • Mass in Kg • Acceleration = m/s2

1 Newton = • Force required to accelerate 1 kilogram of mass at one meter per second for every second

Mass of a small car is 750kg Mass of large car is 1000kg

Small car moves at 2 meters per second for every second •  What is the force? •  750x 2 = •  1500N

Large car moves 2 meters per second for every second •  What is the force? •  1000 X 2 •  2000N

The large car will have more force

Third law of motion Conservation of Momentum

• For every action there is an equal and opposite reaction

Conservation of Momentum

All Forces happen in pairs • Walking • Feet push floor and the floor push feet

Force • Push or pull that starts, stops, or changes the direction of an object

Quick Review • 1st Law = Inertia nd • 2 Law F=M x A rd • 3 Law Equal and Opposite

The End

The Lever Quiz

What class of lever is a prybar?

A •  Pounding a nail •  3rd class

B •  Lifting a nail •  1st Class

C •  Lifting a nail •  2nd class