Lecture_1_2017物理ppt
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n
互相影响
Note on notation: FAB is the force exerted by A on B
Newton’s Third Law, Alternative Statements
n n n
Forces always occur in pairs A single isolated force cannot exist The action force is equal in magnitude to the reaction force and opposite in direction
n
ΣF is the net force
n
This is the vector sum of all the forces acting on the object
n
Newton’s Second Law can be expressed in terms of components:
More About Mass
n
n
n
n n
Mass is an inherent property of an object Mass is independent of the object’s surroundings Mass is independent of the method used to measure it Mass is a scalar quantity The SI unit of mass is kg
Weight will vary with location
一个物体的质量是不会变的,一个scalar【标量】,而其重量是根据引力大小而出来的.
JULIUS SUMNER MILLER VIDEO-N1L [16MIN]
Newton’s Second Law
n
When viewed from an inertial frame, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass
weight不是固定的
n
Weight is not an inherent property of the object
Gravitational Mass vs. Inertial Mass
n
n
n
In Newton’s Laws, the mass is the inertial mass and measures the resistance to a change in the object’s motion In the gravitational force, the mass is determining the gravitational attraction between the object and the Earth Experiments show that gravitational mass and inertial mass have the same value
n
n
Contact forces involve physical contact between two objects Field forces act through empty space
n
No physical contact is required
重力
More About Weight
n
Because it is dependent on g, the weight varies with location
n
g, and therefore the weight, is less at higher altitudes
JULIUS SUMNER MILLER VIDEO- N2L Third Law
n
n
If two objects interact, the force F12 exerted by object 1 on object 2 is equal in magnitude and opposite in direction to the force F21 exerted by object 2 on object 1 F12 = - F21
SUMMARY of Laws
n
n n
1) An object maintains its state of rest or uniform motion unless acted upon by a net external force. 2) F=ma 3) F1,2=- F2,1
Inertia and Mass
n
n
The tendency of an object to resist any attempt to change its velocity is called inertia 惯性 Mass is that property of an object that specifies how much resistance an object exhibits to changes in its velocity
LECTURE 1
"Nature
and Nature's laws lay hid in night: God said, Let Newton be! and all was light".
NEWTONS THREE LAWS (N3L)
The Laws of Motion…
1,惯性定律：一切物体再不受外力作用时,总保持匀速直线运动状态或静止状态. 2,加速度定律：物体运动的加速度与作用在物体上所有外力的合力成正比,与物体的质量 成反比. 3,作用与反作用定律：两物体间的作用力和反作用力总是作用在一条直线上,大小相等方 向相反.
Force
n
Forces are what cause any change in the velocity of an object
Fundamental Forces
n
Gravitational force 重力
n
Between two objects
电磁力
n
Electromagnetic forces
n
Between two charges
核力 亚原子颗粒
n
Nuclear force
n
Between subatomic particles
n
Force is the cause of change in motion, as measured by the acceleration
n
Algebraically, ΣF = m a
More About Newton’s Second Law
n
n
n
One of the forces is the action force, the other is the reaction force 反作用力 作用力 It doesn’t matter which is considered the action and which the reaction The action and reaction forces must act on different objects and be of the same type
（1）一切物体都有保持原有运动状态的特性,即一切物体都有惯性； （2）惯性是物体的固有属性.与物体是否受力、受力大小、是否运动以及运动速度大小等皆无关； （3）质量是惯性大小唯一的量度.即惯性大小只与物体的质量有关.物体的质量越大,惯性越大；反之,也成立； （4）惯性是物体的一种属性,而不是一种力.所以不能说“受到惯性”,只能说“由于惯性”或“某某物体具有惯性”；
独立于物体周围的环境 质量与测量的方法无关 标量【无方向无正负】 国际单位是kg
内在的
vector【矢量】：速度、加速度、位移、力、冲量、动量、电场强度、磁场强度 scalar【标量】：质量、密度、温度、功、能量、路程、速率、体积、时间、热量、电阻等物理量
Mass vs. Weight
n
G=mg weight=mass*9.8N/kg
放射性衰变
n
Weak forces
n
Arise in certain radioactive decay processes
More About Forces
n
n
A spring can be 校正 used to calibrate the magnitude of a force Forces are vectors, so you must use the rules for vector addition to find the net force acting on an object
n n
The object, if at rest, will remain at rest If the object is moving, it will continue to move at a constant velocity
Classes of Forces
n
A force is that which causes an acceleration
n
The net force is the vector sum of all the forces acting on an object
n
Also called total force, resultant force, or unbalanced force
n
Mass and weight are two different quantities Weight is equal to the magnitude of the gravitational force exerted on the object
n
n n n
ΣFx = m ax ΣFy = m ay ΣFz = m az
Units of Force
磅
Gravitational Force
n
n
n
n
The gravitational force, Fg, is the force that the earth exerts on an object This force is directed toward the center of the earth Its magnitude is called the weight of the object Weight = |Fg|= mg
Zero Net Force
n
When the net force is equal to zero:
n n
The acceleration is equal to zero The velocity is constant
n
Equilibrium occurs when the net force is equal to zero
互相影响
Note on notation: FAB is the force exerted by A on B
Newton’s Third Law, Alternative Statements
n n n
Forces always occur in pairs A single isolated force cannot exist The action force is equal in magnitude to the reaction force and opposite in direction
n
ΣF is the net force
n
This is the vector sum of all the forces acting on the object
n
Newton’s Second Law can be expressed in terms of components:
More About Mass
n
n
n
n n
Mass is an inherent property of an object Mass is independent of the object’s surroundings Mass is independent of the method used to measure it Mass is a scalar quantity The SI unit of mass is kg
Weight will vary with location
一个物体的质量是不会变的,一个scalar【标量】,而其重量是根据引力大小而出来的.
JULIUS SUMNER MILLER VIDEO-N1L [16MIN]
Newton’s Second Law
n
When viewed from an inertial frame, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass
weight不是固定的
n
Weight is not an inherent property of the object
Gravitational Mass vs. Inertial Mass
n
n
n
In Newton’s Laws, the mass is the inertial mass and measures the resistance to a change in the object’s motion In the gravitational force, the mass is determining the gravitational attraction between the object and the Earth Experiments show that gravitational mass and inertial mass have the same value
n
n
Contact forces involve physical contact between two objects Field forces act through empty space
n
No physical contact is required
重力
More About Weight
n
Because it is dependent on g, the weight varies with location
n
g, and therefore the weight, is less at higher altitudes
JULIUS SUMNER MILLER VIDEO- N2L Third Law
n
n
If two objects interact, the force F12 exerted by object 1 on object 2 is equal in magnitude and opposite in direction to the force F21 exerted by object 2 on object 1 F12 = - F21
SUMMARY of Laws
n
n n
1) An object maintains its state of rest or uniform motion unless acted upon by a net external force. 2) F=ma 3) F1,2=- F2,1
Inertia and Mass
n
n
The tendency of an object to resist any attempt to change its velocity is called inertia 惯性 Mass is that property of an object that specifies how much resistance an object exhibits to changes in its velocity
LECTURE 1
"Nature
and Nature's laws lay hid in night: God said, Let Newton be! and all was light".
NEWTONS THREE LAWS (N3L)
The Laws of Motion…
1,惯性定律：一切物体再不受外力作用时,总保持匀速直线运动状态或静止状态. 2,加速度定律：物体运动的加速度与作用在物体上所有外力的合力成正比,与物体的质量 成反比. 3,作用与反作用定律：两物体间的作用力和反作用力总是作用在一条直线上,大小相等方 向相反.
Force
n
Forces are what cause any change in the velocity of an object
Fundamental Forces
n
Gravitational force 重力
n
Between two objects
电磁力
n
Electromagnetic forces
n
Between two charges
核力 亚原子颗粒
n
Nuclear force
n
Between subatomic particles
n
Force is the cause of change in motion, as measured by the acceleration
n
Algebraically, ΣF = m a
More About Newton’s Second Law
n
n
n
One of the forces is the action force, the other is the reaction force 反作用力 作用力 It doesn’t matter which is considered the action and which the reaction The action and reaction forces must act on different objects and be of the same type
（1）一切物体都有保持原有运动状态的特性,即一切物体都有惯性； （2）惯性是物体的固有属性.与物体是否受力、受力大小、是否运动以及运动速度大小等皆无关； （3）质量是惯性大小唯一的量度.即惯性大小只与物体的质量有关.物体的质量越大,惯性越大；反之,也成立； （4）惯性是物体的一种属性,而不是一种力.所以不能说“受到惯性”,只能说“由于惯性”或“某某物体具有惯性”；
独立于物体周围的环境 质量与测量的方法无关 标量【无方向无正负】 国际单位是kg
内在的
vector【矢量】：速度、加速度、位移、力、冲量、动量、电场强度、磁场强度 scalar【标量】：质量、密度、温度、功、能量、路程、速率、体积、时间、热量、电阻等物理量
Mass vs. Weight
n
G=mg weight=mass*9.8N/kg
放射性衰变
n
Weak forces
n
Arise in certain radioactive decay processes
More About Forces
n
n
A spring can be 校正 used to calibrate the magnitude of a force Forces are vectors, so you must use the rules for vector addition to find the net force acting on an object
n n
The object, if at rest, will remain at rest If the object is moving, it will continue to move at a constant velocity
Classes of Forces
n
A force is that which causes an acceleration
n
The net force is the vector sum of all the forces acting on an object
n
Also called total force, resultant force, or unbalanced force
n
Mass and weight are two different quantities Weight is equal to the magnitude of the gravitational force exerted on the object
n
n n n
ΣFx = m ax ΣFy = m ay ΣFz = m az
Units of Force
磅
Gravitational Force
n
n
n
n
The gravitational force, Fg, is the force that the earth exerts on an object This force is directed toward the center of the earth Its magnitude is called the weight of the object Weight = |Fg|= mg
Zero Net Force
n
When the net force is equal to zero:
n n
The acceleration is equal to zero The velocity is constant
n
Equilibrium occurs when the net force is equal to zero