Basic Physics Terms
description
Transcript of Basic Physics Terms
![Page 1: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/1.jpg)
![Page 2: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/2.jpg)
Basic Physics TermsIn this lesson, we will review some basic physics terms anddemonstrate them using our Lego gearbox.
• Force and Torque• Mechanical Advantage• Newton’s Laws• Work and Power• Friction
![Page 3: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/3.jpg)
Basic Terms - ForceWhat is a “force?”A force causes something with mass to move (accelerate). This can be summed up with Newton’s 2nd Law. F = m x a
Question: What force do we experience every single day?
Answer: The force of gravity.
(In fact, units of force are called “Newtons.”)
![Page 4: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/4.jpg)
Work is only done by a force on anobject if the force causes the objectto move in the direction of the force.
Objects that are at rest mayhave many forces acting on them,
but no work is doneif there is no movement.
![Page 5: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/5.jpg)
Basic Terms - WorkWork (in physics) is defined as a force acting over a distance.
W = F x d
Work in terms of rotation is a torque acting over an angle.
W = t x q
![Page 6: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/6.jpg)
WorkThe scientific definition of work is
… The transfer of energy through
motion (distance). Work (like energy) is measured in
Joules (J) Formula: W = F * d
![Page 7: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/7.jpg)
Mechanical AdvantageUnderstanding the 2 components of Work is the key tounderstanding mechanical advantage.Question: Where would you hold the wrench for it to be most effective?
![Page 8: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/8.jpg)
Two factors have to be considered when deciding if work is being done….
Was a force applied?
Was there a change in distance?
![Page 9: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/9.jpg)
The SI unit of poweris the Watt,
named in honor ofJames Watt.
One Watt, W, of poweris the power achieved
when 1.0 J of work is done or1.0 J of energy is transferred
in a time of 1.0 s.
![Page 10: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/10.jpg)
Work done against gravity
W = mgh
height object raised (m)
gravity (m/sec2)
work (joules)
mass (g)
![Page 11: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/11.jpg)
![Page 12: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/12.jpg)
In which case would you do more work?
a. lifting 1 book over your head
a. holding 2 books at shoulder level
a. holding a stack of books and walking them to the counter
b. lifting 2 books over your head
b. lifting 2 books over your head
b. pushing a stack of books over to the counter
![Page 13: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/13.jpg)
When doing work problems, what units must be used for . . .Work (W)
Force (F)
Distance (d)
Joule (J)
Newton (N)
meter (M)
![Page 14: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/14.jpg)
![Page 15: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/15.jpg)
![Page 16: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/16.jpg)
The Basics of Machines
![Page 17: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/17.jpg)
Simple Machines“a device that is used to manipulate the
amountand/or direction of force when work is
done”A common misconception is that
machines are used to do a task with less work than would be needed to do the
task without the machine. They do not! In fact (mainly because of friction), you actually do more work with a machine than without it (for the same task).
The major benefit of a machine is thatthe work can be done with less applied
force, but at the expense of the distance through which the force must be applied.
![Page 18: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/18.jpg)
Basic Terms - TorqueWhat is “torque?”
Torque can be thought of as rotational force.
Torque causes something with mass to rotate.
We are interested in “torque” because we deal withrotational motors and axles.
This motor produces a torque.
![Page 19: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/19.jpg)
Force and TorqueHow are force and torque related?
A force here...
…produces atorque here.
moment arm.A force can create a torque by acting through a moment arm.
The relationship is t = F x r. r is the length of the moment arm (in this case, the length of the wrench).
![Page 20: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/20.jpg)
Gears and TorqueUp to now, we have been talking about how gears changespeed. But they can also change torque.
Question: What is the gear ratio of this gear box?
Answer: 75 to 1
That means the last axle rotates 75 times slower than the first axle. It also means the last axle has 75 times the torque as the first axle.
![Page 21: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/21.jpg)
Gears and TorqueWhere does all this “torque” come from?
Consider a pair of gears that are meshed together.
A torque on this axle...
…produces a force at the tooth.
Ft
The moment arm is the radius of the gear.Remember: t = F x r
r
![Page 22: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/22.jpg)
Gears and TorqueThe force from the small gear’s tooth pushes againstthe large gear’s tooth. This creates an equal (and opposite)force in the large gear. This is Newton’s 3rd Law.
…and produces alarger torque on this axle.
F
t
The force acts through this larger moment arm...
r
![Page 23: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/23.jpg)
Gears and Torque
F1 = -F2
t2
r2
t1
r1
Analyzing the forces... t1 = F1 x r1 t2 = F2 x r2
F1 = t1 / r1 F2 = t2 / r2
F1 = - F2
t1 / r1 = -t2 / r2
-t2 / t1 = r2 / r1
The ratio of torques is the ratio of the gear radii.This is the gear ratio!
![Page 24: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/24.jpg)
Gears and TorqueGears can increase the torque (and force) that they exerton something. This is known as mechanical advantage.
BUT, it comes at a price. Do you know what it is?
torque increases
![Page 25: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/25.jpg)
Mechanical Advantage
If you hold the wrench here, you need a lot of force...
If you hold the wrench here, you don’t need as much force...
…but you don’t move very far. …but your hand
moves a long way.
![Page 26: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/26.jpg)
Mechanical AdvantageIt takes the same amount of work to turn the bolt.You can opt for a lot of force and little distance.W = F x d
Or you can choose a little force but a lot of distance.W = f x DIn many of our machines, we want to increase our force, so we don’t mind going the extra distance.
![Page 27: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/27.jpg)
Mechanical AdvantageQuestion: Which ramp would you prefer to use to move a heavy weight to the top of the box?
Answer: This ramp requires less force, but you have to move the weight a longer distance.
![Page 28: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/28.jpg)
Mechanical Advantage
With our gear box, you were able to create a large torque here...
…but you had to turn this handle many times.Remember: W = t x q
![Page 29: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/29.jpg)
Mechanical advantage (MA) is the ratio of output force to input force for a machine. Foutput
MA = Finput
![Page 30: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/30.jpg)
A force of 200 newtons is applied to a machine in order to lift a 1,000-newton load. What is the mechanical advantage of the machine?
MA = 1000 N / 200 N = 5 note no label just five
PROBLEM
![Page 31: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/31.jpg)
PowerPower is the rate at which work is done. It can be thought of as work per second.
Power = Work / sec.Like work, power has 2 components, force and speed.
P = F x v (v stands for velocity).Question: Can you name 2 units for power?
Answer: Horsepower and Watts.
![Page 32: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/32.jpg)
PowerPower has the same trade-offs as work. A motor produces the same amount of power.
So, you can make a robot that’s fast, but weak.
Or you can make a robot that’s slow, but strong.
The total power in must equal the total power out (with an exception)...
![Page 33: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/33.jpg)
Friction = BadFriction is caused by two surfaces rubbing together.
Friction in our gear box causes a loss in the input power. It is lost in the form of heat and sound energy.
![Page 34: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/34.jpg)
Friction = GoodBut friction is also what makes our robot move.
The turning wheel produces a frictional force against the ground, which causes the robot to move.
![Page 35: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/35.jpg)
WHERE ARE WE?• A force causes something with mass to
move.• Torque is rotational force.• Work has 2 components, force and distance.• Mechanical advantage lets you increase
one component of work at the expense of the other.
• Gears are one way to get mechanical advantage. They can increase the robot’s torque.
• Power is the product of force and speed.• A robot can either be slow and strong, or fast
and weak.• Friction causes both losses in power, but
also makes robots move on the ground.
![Page 36: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/36.jpg)
WedgeInclined Plane
Screw
Wheel and Axle
Lever
Pulley
![Page 37: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/37.jpg)
Have you ever tried to unscrew a nut, bolt, or screw from something with your bare hands and discovered that it was just too tight to loosen even if you had a good grip?
![Page 38: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/38.jpg)
You got the proper tool, such as a screw driveror wrench, and unscrewed it!
![Page 39: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/39.jpg)
The wrench and screw driver are examples of a wheel and axle, where the screw or bolt is the axle and the handle is the wheel. The tool makes the job easier by changing the amount of the force you exert.
AxleWheel
![Page 40: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/40.jpg)
All of the simple machines can be used for thousands of jobs
from lifting a 500-pound weight to making a boat go. The
reason why these machines are so special is because they make
difficult tasks much easier.
![Page 41: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/41.jpg)
![Page 42: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/42.jpg)
Fulcrum
Lever
Load
Click Here to Learn More
![Page 43: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/43.jpg)
3 classes of levers
Determined by position of load, fulcrum, and effort
![Page 44: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/44.jpg)
1st Class Lever
The claw on a hammer is a lever. We call this kind of lever a first-class lever.
![Page 45: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/45.jpg)
2nd Class Lever
A bottle opener is a second-class lever, which means the fulcrum is at the end of the lever and the load is in the middle.
![Page 46: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/46.jpg)
3rd Class Lever
A third-class lever has its fulcrum at one end and the load at the other end, with the work you do in the middle. It's how a fishing pole works. You lift just a short distance at the handle, but the end of the pole pops up several feet
![Page 47: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/47.jpg)
![Page 48: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/48.jpg)
A screw is an inclined plane wrapped around a post. Click on the light bulb to learn more.
![Page 49: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/49.jpg)
Two inclined planes make a wedge.
![Page 51: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/51.jpg)
Wheel
Rope This box is easier to lift because of the pulley.
![Page 52: Basic Physics Terms](https://reader035.fdocuments.in/reader035/viewer/2022062302/568163ce550346895dd511d0/html5/thumbnails/52.jpg)