In the force diagram, the length of the line segment is related to the magnitude and proportion of the force.
The answer is no, because the scale of the two diagrams A and B cannot determine whether they are in phase.
With, so can't judge the size of the two forces.
Exercise 45 What would happen to our life without gravity (write a scene you can imagine) (the conclusion is open).
If there is no gravity, objects will be in a state of weightlessness, which is almost always the case for astronauts on spacecraft. Due to gravity, the water will flow downwards and the thrown stones will fall to the ground. These are all familiar phenomena, but if there is no gravity, the state of objects will not be affected by the earth.
At this time, there will be many phenomena in our life: ① people will not fall to the ground after jumping; 2 water can't pour out of the bowl; ③ People can walk upside down; ④ People can swim in the air; 5 strokes can't write; ⑥ Mercury in the thermometer cannot return to the glass bulb.
Exercise 46 To write on a spaceship, you must use a special fountain pen, but you can't write with an ordinary fountain pen. This is because the ink in the fountain pen is in a state of _ _ _ _ _ _ _.
The implicit condition of the analysis is that without gravity, ink cannot flow to the pen tip.
The answer is weightlessness.
Exercise 47 According to "the gravity direction is vertical downward", what questions can be asked (the conclusion is open)?
Analysis as long as the questions raised are related to this conclusion.
Answer (1) What phenomena in daily life indicate that the direction of gravity is vertical downward?
(2) What if the gravity direction is not vertical downward? ...
(3) What are the applications of gravity direction in daily life and production?
Exercise 48 Fill in the blanks with appropriate propositions according to the options:
Proposition: _ _ _ _ _ _. (The conclusion is open)
Option: C A. Train enters the station B. Shot put.
C. the parachutist falls in a straight line at a constant speed.
The ball moves in a uniform circle.
According to Newton's first law, when an object moves in a straight line at a uniform speed, the motion state of the object remains unchanged and the object is subjected to a balancing force.
Answer proposition (1): The following objects move in a straight line at a uniform speed _ _ _ _ _ _.
Proposition (2): The following objects are balanced by _ _ _ _ _ _.
Proposition (3): The motion state of the following objects is _ _ _ _ _ _ _.
Exercise 49. Put a closed transparent box on the left plate of the balance, which contains a bird. When the bird falls on the bottom of the box, the total mass of the bird and the box is 300 g, and the known mass of the box is 200 g. Then, when the bird flies in the box, how many grams should be added to the plate of the balance to keep balance (the conclusion is open).
When the bird moves in the box, the balance state of the balance is different.
Answer (1) When the bird falls on the bottom of the box, the pressure on the balance is equal to the sum of the gravity of the box and the bird.
(2) When the bird flies smoothly in the air in the box, it must constantly flap its wings and press the air downward to obtain the upward force of the air. Only when this force and gravity are balanced can it support its body. In this way, the downward pressure of the wings on the air is transmitted to the bottom of the box through the air, which is equivalent to a bird landing on the bottom of the box. Therefore, the balance is balanced under the condition that the weight of the right disk is constant (that is, 300 g).
(3) If a bird flies violently up or down, its pressure on the air is sometimes greater than the bird's gravity, and sometimes less than the bird's gravity, and the hands of the balance will swing left and right.
Exercise 50 When Xiao Qiang approaches the iron pipe with a magnet, the force on the magnet is _ _ _ _ _ _ _. (The conclusion is open)
The analysis shows that the magnet is supported by gravity and small hands because it is on the ground. A magnet is magnetic because it attracts iron.
The support of the answering hand; Gravity; magnetism
Exercise 5 1 For an electric fan hanging from the ceiling, the tension of the fixed boom is F 1 at rest, and F2 when the electric fan rotates at a constant speed. In both cases, the relationship between F 1 and F2 is _ _ _ _ _ _ _. (Conditions are open).
A.f 1 & gt； The analysis of F2 B.F 1=F2 C.F 1 shows that the forces are mutual. When the fan exhausts downward, the fan is pushed upward by the air. Therefore, the tension of the boom at rest is greater than that at uniform rotation.
The answer is C.
Exercise 52 It is said that a Somali businessman came to the Netherlands and saw that the fish there were very cheap, so he bought 5× 107N fish from fishermen, loaded them on a boat and transported them from the Netherlands near the North Pole to Mogadishu, the Somali capital near the equator. When I got there, I found that 3× 105 N was missing. The ship didn't stop along the way, so it can't be stolen, and the loss in loading and unloading can't be that big.
The gravity of an object measured by a spring scale is related to the position of the object, and the gravity at the poles of the earth is greater than that at the equator.
Gravity is related to the position of an object on the earth, and it is greater near the poles than near the equator.
Exercise 53 If you do a small experiment on a straight train (car or ship), as shown in the figure, let the block in your hand fall freely, then the block will fall in () (conditions are open).
A.A.B.B.C.D. All three situations are possible.
There may be three motion states of the vehicle in a straight line: uniform speed, acceleration and deceleration. If the vehicle slows down, the wood block will fall to point B due to inertia; If the vehicle accelerates, due to inertia, the wood block will fall to point C, so there are three possibilities.
The correct answer is item D.
Exercise 54: The moving car skidded for a certain distance after braking and stopped; Apples falling from trees will fall faster and faster; The football flew over the football player's head and the ball flew out; Weightlifters lift barbells from the ground. Name the physical processes corresponding to these phenomena respectively, and draw a conclusion according to the physical processes corresponding to the above four phenomena. (The conclusion is open)
In these four cases, the change of the object's motion state is due to the action of force, so force is the reason for changing the object's motion state. Apple is falling faster and faster because the potential energy of gravity is converted into kinetic energy, and when the car brakes, kinetic energy is converted into internal energy. Lifting barbells is to convert kinetic energy into potential energy; When a football flies overhead, it first converts kinetic energy into elastic potential energy, and then converts elastic potential energy into kinetic energy, so there is energy conversion or transmission.
The answer sums up four phenomena. Conclusion 1: Force is the reason to change the motion state of an object.
Conclusion 2: Various forms of energy can be transformed or transferred between objects.
Friction is very important to our life. What would our life be like without friction (give three examples) (the conclusion is open)
Answer ① People can't walk normally; 2 hands can't hold a pen to write; (3) The moving car can't stop; Four people can't sit on the stool safely; You can't hold things with chopsticks.
Exercise 56 In the experiment to study what factors are related to the magnitude of sliding friction, why do you have to use a spring dynamometer to pull the block at a uniform speed (the conditions are open)?
An important concept that should be used in this experiment-balancing force is analyzed. Only when moving at a uniform speed can the pull of the spring dynamometer on the wood block be balanced with the friction force, and the reading of the spring dynamometer is equal to the friction force.
The answer is that when moving at a uniform speed, the tension and friction of the spring dynamometer on the wood block are balanced, and the reading of the spring dynamometer is equal to the friction.
Exercise 57 The students of the "Inquiry Learning" research group in a middle school browsed the following article on China Information Network: The Shanghai Pudong maglev train, which started trial operation at the beginning of this year, has a speed of over 300 km/h and no wheels. When running, the body is suspended above the track about 10mm away from the track under the action of electromagnetic force. Accordingly, please analyze what physical knowledge this training contains and briefly explain (conclusion
The analysis of magnetic levitation shows that the magnetic poles with the same name repel each other; The magnetic field is provided by an electromagnet. It is not in contact with the track, so the friction is very small.
The answer is the use of electromagnets; ② Like magnetic poles repel each other; The contact surface is air, so it is not affected by the friction of the track.
The tighter the books on the shelf, the harder it is to take out a book. This is because _ _ _ _ _ _.
The greater the positive pressure, the greater the friction.
Exercise 59 is shown in the picture. Please name at least five physical principles (including structure and use) that should be applied to bicycles. Each physical principle can only be used once and cannot be repeated. If the bell applies the lever principle, other parts (such as brakes) will be out of the question. (The conclusion is open)
Answer (1) Pedal, crank and sprocket-a labor-saving axle. (2) Bell spring-reset by the elastic potential energy of the spring.
(3) The tread pattern increases the static friction between the tire and the ground.
(4) Ball of each shaft-replacing sliding friction with rolling friction.
(5) Rubber handlebars-The heat transfer performance of rubber is poor, so the handlebars are not cold in winter and not hot in summer.
(6) Mudguard-inertia.
(7) Inflating tires-using the relationship between air pressure and volume.
Exercise 60 Release an object from a height. Under the action of gravity, the object moves freely vertically downward. We call this kind of motion free fall. Of course, the real free fall can only happen in a space without air. But in daily life, under certain conditions, the air resistance is small, so we can also approximately regard the falling motion of daily objects as free falling motion.
In order to study the relationship between the motion speed and the motion time of an object in the process of free fall, Xiao Ming made a free fall experiment with a small ball and got a group.
The experimental data are as follows:
Exercise time
1
2
three
Motion speed v (m/s)
10
20
30
According to the above data, what conclusion can you draw (information given)
From the analysis of the data in the table, it can be seen that the speed of the ball is different at different times, and the speed of the ball increases with the increase of time; It can also be seen from the table that in the same time period, the change value of speed is the same, so different conclusions can be drawn.
Answer ① The longer the ball falls, the greater the speed; ② The change value of ball speed per unit time is the same.
Exercise 6 1 skating has a lot of physical knowledge. Please name two knowledge points at will (conclusion is open):
( 1)__________.(2)__________,
Answer (1) inertia; (2) The smoother the surface, the smaller the friction; (3) reduce the stress area and increase the pressure; (4) Force causes the object to change its motion state, etc.
Exercise 62 If the object moves in a straight line at a uniform speed, then () (The conclusion is open)
A. the resultant force on an object must be zero.
B. an object can only be acted by a pair of balancing forces.
C. the internal energy of an object may increase.
D. the mechanical energy of the object will increase.
The condition of uniform motion of an object is that the resultant force on the object must be zero. If an object is rubbed, the internal energy may increase; When the motion position of an object increases, the mechanical energy increases.
Answer a, c and d
You can have a general look, and if they are the same, you can list the topics you don't understand. We can help you solve it.
Exercise 44 has two forces, one is long and the other is short, as shown in Figures A and B. Can you tell which force is the greater? Why (conditions are open)?
In the force diagram, the length of the line segment is related to the magnitude and proportion of the force.
The answer is no, because the scale of the two diagrams A and B cannot determine whether they are in phase.
With, so can't judge the size of the two forces.
Exercise 45 What would happen to our life without gravity (write a scene you can imagine) (the conclusion is open).
If there is no gravity, objects will be in a state of weightlessness, which is almost always the case for astronauts on spacecraft. Due to gravity, the water will flow downwards and the thrown stones will fall to the ground. These are all familiar phenomena, but if there is no gravity, the state of objects will not be affected by the earth.
At this time, there will be many phenomena in our life: ① people will not fall to the ground after jumping; 2 water can't pour out of the bowl; ③ People can walk upside down; ④ People can swim in the air; 5 strokes can't write; ⑥ Mercury in the thermometer cannot return to the glass bulb.
Exercise 46 To write on a spaceship, you must use a special fountain pen, but you can't write with an ordinary fountain pen. This is because the ink in the fountain pen is in a state of _ _ _ _ _ _ _.
The implicit condition of the analysis is that without gravity, ink cannot flow to the pen tip.
The answer is weightlessness.
Exercise 47 According to "the gravity direction is vertical downward", what questions can be asked (the conclusion is open)?
Analysis as long as the questions raised are related to this conclusion.
Answer (1) What phenomena in daily life indicate that the direction of gravity is vertical downward?
(2) What if the gravity direction is not vertical downward? ...
(3) What are the applications of gravity direction in daily life and production?
Exercise 48 Fill in the blanks with appropriate propositions according to the options:
Proposition: _ _ _ _ _ _. (The conclusion is open)
Option: C A. Train enters the station B. Shot put.
C. the parachutist falls in a straight line at a constant speed.
The ball moves in a uniform circle.
According to Newton's first law, when an object moves in a straight line at a uniform speed, the motion state of the object remains unchanged and the object is subjected to a balancing force.
Answer proposition (1): The following objects move in a straight line at a uniform speed _ _ _ _ _ _.
Proposition (2): The following objects are balanced by _ _ _ _ _ _.
Proposition (3): The motion state of the following objects is _ _ _ _ _ _ _.
Exercise 49. Put a closed transparent box on the left plate of the balance, which contains a bird. When the bird falls on the bottom of the box, the total mass of the bird and the box is 300 g, and the known mass of the box is 200 g. Then, when the bird flies in the box, how many grams should be added to the plate of the balance to keep balance (the conclusion is open).
When the bird moves in the box, the balance state of the balance is different.
Answer (1) When the bird falls on the bottom of the box, the pressure on the balance is equal to the sum of the gravity of the box and the bird.
(2) When the bird flies smoothly in the air in the box, it must constantly flap its wings and press the air downward to obtain the upward force of the air. Only when this force and gravity are balanced can it support its body. In this way, the downward pressure of the wings on the air is transmitted to the bottom of the box through the air, which is equivalent to a bird landing on the bottom of the box. Therefore, the balance is balanced under the condition that the weight of the right disk is constant (that is, 300 g).
(3) If a bird flies violently up or down, its pressure on the air is sometimes greater than the bird's gravity, and sometimes less than the bird's gravity, and the hands of the balance will swing left and right.
Exercise 50 When Xiao Qiang approaches the iron pipe with a magnet, the force on the magnet is _ _ _ _ _ _ _. (The conclusion is open)
The analysis shows that the magnet is supported by gravity and small hands because it is on the ground. A magnet is magnetic because it attracts iron.
The support of the answering hand; Gravity; magnetism
Exercise 5 1 For an electric fan hanging from the ceiling, the tension of the fixed boom is F 1 at rest, and F2 when the electric fan rotates at a constant speed. In both cases, the relationship between F 1 and F2 is _ _ _ _ _ _ _. (Conditions are open).
A.f 1 & gt； The analysis of F2 B.F 1=F2 C.F 1 shows that the forces are mutual. When the fan exhausts downward, the fan is pushed upward by the air. Therefore, the tension of the boom at rest is greater than that at uniform rotation.
The answer is C.
Exercise 52 It is said that a Somali businessman came to the Netherlands and saw that the fish there were very cheap, so he bought 5× 107N fish from fishermen, loaded them on a boat and transported them from the Netherlands near the North Pole to Mogadishu, the Somali capital near the equator. When I got there, I found that 3× 105 N was missing. The ship didn't stop along the way, so it can't be stolen, and the loss in loading and unloading can't be that big.
The gravity of an object measured by a spring scale is related to the position of the object, and the gravity at the poles of the earth is greater than that at the equator.
Gravity is related to the position of an object on the earth, and it is greater near the poles than near the equator.
Exercise 53 If you do a small experiment on a straight train (car or ship), as shown in the figure, let the block in your hand fall freely, then the block will fall in () (conditions are open).
A.A.B.B.C.D. All three situations are possible.
There may be three motion states of the vehicle in a straight line: uniform speed, acceleration and deceleration. If the vehicle slows down, the wood block will fall to point B due to inertia; If the vehicle accelerates, due to inertia, the wood block will fall to point C, so there are three possibilities.
The correct answer is item D.
Exercise 54: The moving car skidded for a certain distance after braking and stopped; Apples falling from trees will fall faster and faster; The football flew over the football player's head and the ball flew out; Weightlifters lift barbells from the ground. Name the physical processes corresponding to these phenomena respectively, and draw a conclusion according to the physical processes corresponding to the above four phenomena. (The conclusion is open)
In these four cases, the change of the object's motion state is due to the action of force, so force is the reason for changing the object's motion state. Apple is falling faster and faster because the potential energy of gravity is converted into kinetic energy, and when the car brakes, kinetic energy is converted into internal energy. Lifting barbells is to convert kinetic energy into potential energy; When a football flies overhead, it first converts kinetic energy into elastic potential energy, and then converts elastic potential energy into kinetic energy, so there is energy conversion or transmission.
The answer sums up four phenomena. Conclusion 1: Force is the reason to change the motion state of an object.
Conclusion 2: Various forms of energy can be transformed or transferred between objects.
Friction is very important to our life. What would our life be like without friction (give three examples) (the conclusion is open)
Answer ① People can't walk normally; 2 hands can't hold a pen to write; (3) The moving car can't stop; Four people can't sit on the stool safely; You can't hold things with chopsticks.
Exercise 56 In the experiment to study what factors are related to the magnitude of sliding friction, why do you have to use a spring dynamometer to pull the block at a uniform speed (the conditions are open)?
An important concept that should be used in this experiment-balancing force is analyzed. Only when moving at a uniform speed can the pull of the spring dynamometer on the wood block be balanced with the friction force, and the reading of the spring dynamometer is equal to the friction force.
The answer is that when moving at a uniform speed, the tension and friction of the spring dynamometer on the wood block are balanced, and the reading of the spring dynamometer is equal to the friction.
Exercise 57 The students of the "Inquiry Learning" research group in a middle school browsed the following article on China Information Network: The Shanghai Pudong maglev train, which started trial operation at the beginning of this year, has a speed of over 300 km/h and no wheels. When running, the body is suspended above the track about 10mm away from the track under the action of electromagnetic force. Accordingly, please analyze what physical knowledge this training contains and briefly explain (conclusion
The analysis of magnetic levitation shows that the magnetic poles with the same name repel each other; The magnetic field is provided by an electromagnet. It is not in contact with the track, so the friction is very small.
The answer is the use of electromagnets; ② Like magnetic poles repel each other; The contact surface is air, so it is not affected by the friction of the track.
The tighter the books on the shelf, the harder it is to take out a book. This is because _ _ _ _ _ _.
The greater the positive pressure, the greater the friction.
Exercise 59 is shown in the picture. Please name at least five physical principles (including structure and use) that should be applied to bicycles. Each physical principle can only be used once and cannot be repeated. If the bell applies the lever principle, other parts (such as brakes) will be out of the question. (The conclusion is open)
Answer (1) Pedal, crank and sprocket-a labor-saving axle. (2) Bell spring-reset by the elastic potential energy of the spring.
(3) The tread pattern increases the static friction between the tire and the ground.
(4) Ball of each shaft-replacing sliding friction with rolling friction.
(5) Rubber handlebars-The heat transfer performance of rubber is poor, so the handlebars are not cold in winter and not hot in summer.
(6) Mudguard-inertia.
(7) Inflating tires-using the relationship between air pressure and volume.
Exercise 60 Release an object from a height. Under the action of gravity, the object moves freely vertically downward. We call this kind of motion free fall. Of course, the real free fall can only happen in a space without air. But in daily life, under certain conditions, the air resistance is small, so we can also approximately regard the falling motion of daily objects as free falling motion.
In order to study the relationship between the motion speed and the motion time of an object in the process of free fall, Xiao Ming made a free fall experiment with a small ball and got a group.
The experimental data are as follows:
Exercise time
1
2
three
Motion speed v (m/s)
10
20
30
According to the above data, what conclusion can you draw (information given)
From the analysis of the data in the table, it can be seen that the speed of the ball is different at different times, and the speed of the ball increases with the increase of time; It can also be seen from the table that in the same time period, the change value of speed is the same, so different conclusions can be drawn.
Answer ① The longer the ball falls, the greater the speed; ② The change value of ball speed per unit time is the same.
Exercise 6 1 skating has a lot of physical knowledge. Please name two knowledge points at will (conclusion is open):
( 1)__________.(2)__________,
Answer (1) inertia; (2) The smoother the surface, the smaller the friction; (3) reduce the stress area and increase the pressure; (4) Force causes the object to change its motion state, etc.
Exercise 62 If the object moves in a straight line at a uniform speed, then () (The conclusion is open)
A. the resultant force on an object must be zero.
B. an object can only be acted by a pair of balancing forces.
C. the internal energy of an object may increase.
D. the mechanical energy of the object will increase.
The condition of uniform motion of an object is that the resultant force on the object must be zero. If an object is rubbed, the internal energy may increase; When the motion position of an object increases, the mechanical energy increases.
Answer a, c and d