Lecture 21 Using Machines Ozgur Unal NIS – PHYSICAL SCIENCE Lecture 21 Using Machines Ozgur Unal

Machines A machine is a device that makes doing work easier. Try to explain how the machines you see in front of you help you do work easier.

Making Work Easier There are three main ways machines help us do work easier: Increasing the force applied. Increasing the distance over which a force can be applied. Changing the direction of the force applied. Increasing force: Example: A car jack

Force and Distance: Example: A ramp Making Work Easier Force and Distance: Example: A ramp Changing Direction: Example: An ax blade

The Work Done by Machines Consider the wheelbarrow in the picture. What is the advantage of using this wheelbarrow? What is the force you apply on the wheelbarrow? What is the force that wheelbarrow applies on the load? The force that is applied to a machine is called the input force (Fin). The force applied by a machine is called the output force (Fout).

The Work Done by Machines Remember the definition fo work Work = Force * Distance Two kinds of work need to be considered for machines: Work done by you on the machine: Win = Fin * din Work done by the machine: Wout = Fout * dout

Conserving Energy Remember the law of conservation of energy. The work done on a machine is the energy transferred to the machine. The work done by the machine cannot be greater than this energy transferred. However, the energy transferred might be lost in the form of heat due to friction. Therefore, for real machines work done my the machine is always lower than the work done on the machine. This is due to friction.

Ideal Machines Suppose a perfect machine without friction could be built. In this machine Win would be equal to Wout. If Win = Wout, then you have an ideal machine. Ideal machines are machines where there is no friction. Example: Suppose the hammer claw (assume it is an ideal machine) in Figure 10 moves a distance of 1 cm to remove a nail. If an output force of 1,500 N is exerted by the claw of the hammer and you move the handle of the hammer by 5 cm, find the input force. Win = Wout Fin * din = Fout * dout

IMA = Fout / Fin = din / dout Mechanical Advantage Some machines, such as a wheelbarrow, do work easier by making the output force greater than the input force. The ratio of the output force to the input force is the mechanical advantage of a machine. MA = Fout / Fin Example: What is the MA of the hammer in Figure 10? Ideal mechanical advantage: The mechanical advantage of an ideal machine is called ideal mechanical advantage (IMA). IMA can be calculated by dividing the input distance by the output distance. IMA = Fout / Fin = din / dout

Efficiency = 100 % * Wout / Win Ideal machines have no friction. But all the machines in real life have friction. For this reason, the Wout of a machine is always less than Win. Efficiency is a measure of how much of the work put into a machine is changed into useful output work by the machine. A machine with high efficiency (meaning less friction) produces less thermal energy. Efficiency = 100 % * Wout / Win You already studied friction, try to answer the following question: How can you increase efficiency of a machine?

Leonardo da Vinci A great artist but also a great inventor of extraordinary collection of machines! Research Leonardo da Vinci and his inventions.

Lecture 22 Simple Machines Ozgur Unal NIS – PHYSICAL SCIENCE Lecture 22 Simple Machines Ozgur Unal

Simple Machines A simple machine is a machine that does work with only one movement of the machine. There are six types of simple machines: Lever Pulley Wheel and axle Inclined plane Screw Wedge

Levers A lever is a bar that is free to pivot or turn around a fixed point. The fixed point the lever pivots on is called fulcrum. Output arm and input arm. If output arm is longer than the input arm, the output force will be less than than put force (law of conservation of energy) IMA = Fout / Fin = Lin / Lout Three classes of levers: 1st class, 2nd class and 3rd class.

First Class Lever For a first class lever, fulcrum is located between the input and output forces. Example: Screw driver used to open a paint can IMA of first class levers can be less than, equal to or greater than 1.

Second Class Lever For a second class lever, the output force is located between the input force and the fulcrum. Example: Wheelbarrow IMA of second class levers is always greater than 1.

Third Class Lever For a third class lever, the input force is located between the output force and the fulcrum. Example: Baseball bat IMA of third class levers is always less than 1.

Pulleys A pulley is a grooved wheel with a rope, chain or cable along a groove. A system of pulleys can change the direction of the input force and make the output force larger. We can classify pulleys into three: Fixed pulleys Movable pulleys The block and tackle

Pulleys Fixed Pulleys: A fixed pulley is attached to something that doesn’t move, such as a ceiling or wall. Fixed pulleys only change the direction of force, IMA is 1. The distance you pull the rope equals the distance the weight moves.

Pulleys Movable Pulleys: A pulley in which one end of the rope is fixed and the wheel is free to move is called a movable pulley. IMA of movable pulleys is 2. The distance you pull the rope is twice the distance the weight moves.

Pulleys The Block and Tackle: A system of pulleys consisting of fixed and movable pulleys is called a block and tackle. IMA is equal to the number of ropes that support the weight. IMA of block and tackle can be increased by increaing the number of pulleys in the pulley system.

Wheel and Axle What is the advantage of using this door handle? If you tried to open it without the handle, would it be easier? A wheel and axle is a simple machine consisting of a shaft or axle attached to the center of a larger wheel, so that the wheel and axle rotate together. A wheel and axle is a modified lever.

Examples of wheel and axle: Doorknobs, screwdrivers, gears IMA = radius of wheel / radius of axle = rw / ra Input force acts on the wheel, output force acts on the axle. IMA can be increased by increasing the radius of the wheel.

IMA = length of slope / height of slope = l / h Inclined Planes An inclined plane is a sloping surface that reduces the amount of force required to do work. IMA = length of slope / height of slope = l / h IMA can be increased by making the plane longer for a given height. Example: Ramp

The Screw A screw is an inclined plane wrapped in a spiral around a cylindrical post. Examples: Screw, jar lids, cork screw, spiral stair case. IMA of a screw depends on the spacing of the threads. If IMA is larger, more turns are required to drive it into a material.

The Wedge A wedge is an inclined plane with one or more sloping sides. It changes the direction of the input force. Example: Knife, ax blade, zipper IMA of a wedge is calculated by dividing the length of one side of the wedge by the width of the wedge at the thick end.

Compound Machines Two or more simple machines operate together form a compound machine. Example: Scissor, bicycle Identify the simple machines in a bicycle and a scissor.

Leonardo da Vinci Helicopter

Leonardo da Vinci

Leonardo da Vinci Glider