1
Cooking in an electric cooker, cooking in an electric wok and boiling water in an electric kettle all convert electric energy into internal energy.
Cooking, cooking and boiling water by heat transfer.
2
Exhaust fan (range hood) converts electric energy into mechanical energy and uses air convection to ventilate.
Change.
three
Three-hole plugs of rice cookers, electric cookers and electric kettles are inserted into three hole socket to prevent electric leakage.
And the occurrence of electric shock accidents.
four
The microwave oven has the advantages of uniform heating, high thermal efficiency, sanitation and no pollution. The principle of heating is to use electric energy to convert it into
Electromagnetic energy, and then convert electromagnetic energy into internal energy.
five
The electric lamp in the kitchen works by converting electric energy into internal energy and light energy by the thermal effect of current.
six
Kitchen stoves (honeycomb coal stove, liquefied gas stove, coal stove and wood stove) convert chemical energy into internal energy.
Energy, that is, the heat released by fuel combustion.
Second, phenomena related to mechanical knowledge.
1
The spout and belly of the electric kettle form a communication device, and the water surface is always flat.
2
The thin edge of the kitchen knife is to reduce the stress area and increase the pressure.
three
The blade of the kitchen knife has oil to make the contact surface smooth and reduce friction when cutting vegetables.
four
The handle, spatula handle and electric kettle handle have convex and concave patterns, which make the contact surface rough and increase friction.
five
When the fire shovel delivers coal, the inertia of coal is used to deliver coal into the furnace.
six
Pour boiling water into a thermos and know the water level according to the sound. Due to the increase of water, the length of the air column
The lower the degree, the higher the vibration frequency and the greater the tone.
seven
When grinding the kitchen knife, water it constantly, because the heat generated by the friction between the kitchen knife and the stone increases the internal energy of the knife.
With the increase of temperature, the hardness of the knife edge becomes smaller and the knife edge is unfavorable; Watering reduces the internal energy of kitchen knife by heat transfer.
When the temperature drops, it will not rise too high.
Third, phenomena related to thermal knowledge.
(a) Phenomena related to thermal expansion and heat transfer.
1
When boiling water or cooking with a stove, put the bottom of the pot on the outer flame of the flame, and don't let the bottom of the pot hold down the fire.
The temperature of the pot rises rapidly because the outer flame temperature of the flame is high.
2
The handles of cookers such as spatula, spoon, colander and aluminum pot are all made of wood, because wood is hot.
Good conductor, so as not to burn your hands when cooking.
three
The purpose of installing an exhaust fan above the cooker is to accelerate air convection and exhaust kitchen fumes in time.
Avoid polluting the space.
four
Hot casseroles are easily broken in wetlands. This is because casserole is a bad conductor of heat.
When placed on a wetland,
The outer wall of casserole shrinks rapidly, and the inner wall temperature drops slowly.
Uneven contraction inside and outside the casserole,
Therefore, it is easy to break.
five
When the thermos bottle is full of boiling water, it can keep the temperature better if it is not full. Because when it is not full, there is a layer on the bottle mouth.
Air is a bad conductor of heat, which can better prevent heat loss.
six
Cooking mainly uses heat conduction to transfer heat, while cooking and boiling water mainly use convection to transfer heat.
13
Calculation of speed, distance and time; Description of reference object and motion state
14
Know the signs such as speed limit, mileage and no-ringing, and understand their meanings.
Second, acoustics.
1
The car horn should ring, and try to eliminate the sound of the engine (the engine is equipped with a silencer)—
This is to reduce the noise at the sound source.
2
In order to reduce the impact of vehicle noise on roadside residents, barriers are set up or trees are planted on the roadside.
So as to reduce the noise in the propagation process.
three
Speaker sound: electric energy-mechanical energy
Third, heat dissipation.
1
Automobile engines Diesel engines or gasoline engines-they are internal combustion engines-use internal energy to do work.
2
The engine is equipped with a water jacket, and circulating water is used to help the engine dissipate heat-water has a large specific heat capacity.
three
In winter, in order to prevent the water tank from freezing, the water in the water tank should be discharged at night to prevent the harm of heat expansion and cold contraction.
four
A series of heating wires are embedded in the glass plate of the rear window of the car-it can prevent the formation of fog in the car.
Attached to the glass and condensed.
five
When you just get on the bus or a car passes by you, you will smell a strong smell of gasoline-diffusion.
six
Air-conditioned car window glass is designed as a double layer to prevent heat transfer.
seven
The use of gas fuel in environment-friendly cars can reduce the pollution to the atmosphere.
Fourth, electrical aspects.
1
The engine of a car is usually started by a low-voltage motor: the motor is based on the effect of magnetic field on current.
Made of ... that converts electrical energy into mechanical energy when working.
2
Automobile motor (automobile motor) is usually powered by on-board battery (storage battery), which can be used during automobile operation.
The vehicle-mounted generator is driven by wheels to generate electricity,
Charge the battery.
When charging the battery,
Electric energy conversion
Store chemical energy,
At this time, the battery is an electrical appliance;
When the battery is used to supply power to the motor,
Chemical energy conversion
Convert it into electric energy, and the battery is the power supply.
three
Car batteries are also used in air conditioners, fans, tape recorders,
laser record
Machines and various uses
Electric energy can be easily converted into mechanical energy, acoustic energy, light energy, etc.
three
A chain is usually hung at the tail of a tanker to reach the road surface, which is beneficial to make it bumpy during transportation.
The charge generated by air separation is quickly transmitted to the earth to avoid the disaster caused by electrostatic discharge.
four
Light emission: electric energy-light energy
Verb (abbreviation for verb) optical aspect
1
The rearview mirror beside the car and the observation mirror at the intersection are convex mirrors, which can broaden the field of vision.
2
When the car is driving at night, the lights are generally not turned on in the car, which can prevent the passengers in the car from blocking the wind in front of the driver.
The image on the glass will interfere with the driver's correct judgment
three
The windshield in front of a car is usually not upright (except for cars with high chassis) because of the windshield.
It is equivalent to a flat mirror, through which the objects in the car are easily imaged in front of the driver, which affects the driver's judgment.
four
Automobile taillight lampshade: the corner reflector can reflect the incoming light to ensure the safety of the vehicles behind.
five
Car headlights: concave mirror reflection principle, the short-distance filament is near the focus, and the long-distance filament is at the focus.
Physical knowledge on bicycles
Do you know what physical knowledge there is on the bike? Let's have a look.
1
Knowledge of bicycle friction.
① Why do bicycle tires have uneven patterns?
Friction is related to two factors: pressure and roughness of contact surface. The greater the pressure, mo.
The greater the friction; The rougher the contact surface, the greater the friction. It is common for bicycle tires to have uneven patterns.
By increasing the roughness between the bicycle and the ground,
To increase friction,
Its purpose is to prevent bicycles.
Slip and fall.
② Why can bicycles go forward?
When we ride a bike,
Because people and bicycles put pressure on the ground,
The tire is not smooth with the ground,
Therefore, there is friction between the bicycle and the road surface.
however
Why can a bicycle go forward? This still depends on the rear wheel.
Friction with the ground,
The direction of friction is forward.
The friction of the front wheel is dry.
What is that? Hinder the movement of the car!
Its direction is opposite to that of the bicycle.
These two forces are equal in magnitude,
The direction is opposite, so the bicycle moves at a constant speed. However, when people push bicycles forward on the ground, the front wheels
The friction direction of the rear wheel is backward. Then who is balancing these two forces? The friction between the foot and the ground is forward!
③ Why can a bicycle stop after braking?
When braking, the friction between the brake shoe and the rim will hinder the rotation of the rear wheel. The greater the hand pressure, the brake shoe will point at the car.
The greater the pressure of the ring, the greater the friction and the slower the rotation of the rear wheel. If it is fully braked,
At this time, the friction between the rear wheel and the ground becomes sliding friction (originally rolling friction, forward direction).
The direction was backward, which hindered the movement of the bicycle, so it stopped.
(4) Where are the steel balls installed on the bicycle? Why Zhu Gang?
There are steel balls in the front axle, middle axle, rear axle, handlebar rotation and pedal rotation of bicycles.
People always want to relax when riding a bike.
Flexible,
Save effort.
Rolling can greatly reduce friction, not sliding.
Friction,
So steel balls need to be installed where the bicycle rotates.
We can add lubricating oil at any time,
interface
Stay away from each other, so that the friction can be reduced.
2
Knowledge of lever and axle of bicycle.
(1) lever on bicycle
A
Lever to control the steering of the front wheel: The handlebar of a bicycle is a labor-saving lever, and people can turn it with little force.
Move the front wheel of the bicycle to control the movement direction and balance of the bicycle.
B
Brake lever: The brake handle on the handlebar is a labor-saving lever, so people can brake with little force.
Press the rim with more pressure.
② Axles on bicycles.
A
Pedal and thumbwheel on the central shaft: form a labor-saving wheel shaft (the pedal radius is greater than the thumbwheel radius).
B
Bicycle handlebar and front fork axle: form a labor-saving axle (the turning radius of handlebar is greater than the radius of front fork axle).
C
Gears on the rear axle and rear wheel: form a laborious axle (the radius of the gear is smaller than the radius of the rear wheel).
three
Knowledge of bicycle air pressure.
Inflating the inner tube of bicycle: All kinds of early wheels were wooden wheels and iron wheels, which were uneven. The use of modern bicycles
Inflatable inner tube mainly increases the pressure in the fetus,
Can play a buffering role,
At the same time, it can reduce bicycles.
Resistance to progress.
Function of valve core: The valve core on the inflatable inner tube acts as a one-way valve, allowing only gas to enter, but not gas.
Let the gas leak out, facilitate air intake, and ensure the tightness of the inflatable inner tube.
four
Optical knowledge on bicycles.
The red taillight on the bicycle,
Will not glow by itself,
But at night, you can remind the driver.
because
The taillights of bicycles are made up of many honeycomb-shaped "cells", and each "cell" is made up of three cells.
success
90
Degree of reflecting surface.
So at night,
When the light of the car behind hits the taillight of the bicycle,
It will produce reflected light, which can attract the driver's attention because of its striking red color.
Bicycle is a very popular means of transportation in China.
In its
"body"
Used a lot of mechanical knowledge.
1
Application in measurement
When measuring the length of the runway, you can use a bicycle. For example, the diameter of an ordinary wheel is
0.7 1
Rice or
0.66
rice.
Then the length of a circle is the diameter times π.
Pi?
Yue Ji
2.23
Rice or
2.07
Rice,
Then,
Let the car follow
The runway rolls and records the number of laps.
n
, runway length is
n
×
2.23
Rice or
n
×
2.07
rice.
2
Application of force and motion
( 1)
Reduce and increase friction.
The front axle of a car,
Both the center axle and the rear axle roll to reduce friction.
To further reduce friction,
People often
Lubricate these parts.
Many places are engraved with uneven patterns to increase friction. Such as tires, plastic handle covers, pedal covers and brakes.
Wait for the cover Changing rolling friction into sliding friction to increase friction. For example, when braking, the wheels stop rolling, but instead
Sliding on the ground greatly increases the friction, so the car can stop quickly. Hold your hands tightly when braking.
Brake handle, increase the pressure of brake shoe on steel ring, and make the wheel stop rolling.
(2)
Damping effect of spring.
There are many springs under the car seat cushion to absorb shock.
three
Application of stress knowledge
( 1)
Bicycle tires are engraved with loads. If the vehicle is too heavy, the tires will be crushed due to excessive pressure.
(2)
The seat cushion is saddle-shaped, which can increase the contact area between the seat cushion and the human body to reduce the pressure on the buttocks, thus,
People don't feel tired easily when riding bicycles.
four
Application of simple mechanical knowledge
The brake handle and connecting rod in the bicycle brake system are labor-saving levers,
The tension on the brake shoe can be increased.
oneself
In order to save labor or distance,
Axles are also used for:
Pedal and sprocket tooth plate;
Rear wheel, flywheel and faucet
And a rotating shaft.
five
Knowledge application of work and mechanical energy
( 1)
According to the principle of work: saving effort will consume distance. Therefore, when people go uphill, they often ride "
S
Form a "route".
That's the truth.
(2)
Conversion between kinetic energy and gravitational potential energy.
For example, before riding uphill,
People often have to step on the pedal a few times.
It's easier to get up,
Here is the conversion of kinetic energy into potential energy.
And riding downhill without pedaling, the speed is getting faster and faster, which is the conversion of potential energy into kinetic energy.
six
Application of Inertia Law
A fast bike,
If the front wheels suddenly brake,
Why does the rear wheel jump?
This is because the front wheel
Because the resistance suddenly stops moving,
But neither the man nor the rear wheel resisted.
According to the law of inertia,
mankind
And the rear wheel should go straight ahead, so that the rear wheel will jump.
Remember not to use the bicycle front brake alone when driving downhill or at high speed, otherwise a rollover accident will occur!