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Newton’s second law of motion is more than a definition; it is a relationship among acceleration, force, and mass. It can help us make predictions. Each of those physical quantities can be defined independently, so the second law tells us something basic and universal about nature. The next section introduces the third and final law of motion.

Section summary

  • Acceleration, a size 12{ { {a}} sup { ' }>a} {} , is defined as a change in velocity, meaning a change in its magnitude or direction, or both.
  • An external force is one acting on a system from outside the system, as opposed to internal forces, which act between components within the system.
  • Newton’s second law of motion states that the acceleration of a system is directly proportional to and in the same direction as the net external force acting on the system, and inversely proportional to its mass.
  • In equation form, Newton’s second law of motion is a = F net m size 12{a= { {F rSub { size 8{"net"} } } over {m} } } {} .
  • This is often written in the more familiar form: F net = m a size 12{F rSub { size 8{"net"} } =ma} {} .
  • The weight w size 12{w} {} of an object is defined as the force of gravity acting on an object of mass m size 12{m} {} . The object experiences an acceleration due to gravity g size 12{g} {} :

    w = m g size 12{w=mg} {} .

  • If the only force acting on an object is due to gravity, the object is in free fall.
  • Friction is a force that opposes the motion past each other of objects that are touching.

Conceptual questions

Which statement is correct? (a) Net force causes motion. (b) Net force causes change in motion. Explain your answer and give an example.

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Why can we neglect forces such as those holding a body together when we apply Newton’s second law of motion?

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Explain how the choice of the “system of interest” affects which forces must be considered when applying Newton’s second law of motion.

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Describe a situation in which the net external force on a system is not zero, yet its speed remains constant.

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A system can have a nonzero velocity while the net external force on it is zero. Describe such a situation.

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A rock is thrown straight up. What is the net external force acting on the rock when it is at the top of its trajectory?

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(a) Give an example of different net external forces acting on the same system to produce different accelerations. (b) Give an example of the same net external force acting on systems of different masses, producing different accelerations. (c) What law accurately describes both effects? State it in words and as an equation.

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If the acceleration of a system is zero, are no external forces acting on it? What about internal forces? Explain your answers.

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If a constant, nonzero force is applied to an object, what can you say about the velocity and acceleration of the object?

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The gravitational force on the basketball in [link] is ignored. When gravity is taken into account, what is the direction of the net external force on the basketball—above horizontal, below horizontal, or still horizontal?

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Problem exercises

You may assume data taken from illustrations is accurate to three digits.

A 63.0-kg sprinter starts a race with an acceleration of 4 . 20 m /s 2 size 12{4 "." "20"" m/s" rSup { size 8{2} } } {} . What is the net external force on him?

265 N

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If the sprinter from the previous problem accelerates at that rate for 20 m, and then maintains that velocity for the remainder of the 100-m dash, what will be his time for the race?

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Questions & Answers

a thick glass cup cracks when hot liquid is poured into it suddenly
Aiyelabegan Reply
because of the sudden contraction that takes place.
railway crack has gap between the end of each length because?
Aiyelabegan Reply
For expansion
Please i really find it dificult solving equations on physic, can anyone help me out?
Big Reply
what is the equation?
fersnels biprism spectrometer how to determined
Bala Reply
how to study the hall effect to calculate the hall effect coefficient of the given semiconductor have to calculate the carrier density by carrier mobility.
what is the difference between atomic physics and momentum
Nana Reply
find the dimensional equation of work,power,and moment of a force show work?
Emmanuel Reply
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Michelson Morley experiment
Riya Reply
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Calculate the final velocity attained, when a ball is given a velocity of 2.5m/s, acceleration of 0.67m/s² and reaches its point in 10s. Good luck!!!
Eklu Reply
vf=vi+at vf=2.5+ 0.67*10 vf= 2.5 + 6.7 vf = 9.2
s = vi t +1/2at sq s=58.5 s=v av X t vf= 9.2
how 2.68
v=u+at where v=final velocity u=initial velocity a=acceleration t=time
the answer is 9.2m/s
express your height in Cm
Emmanuel Reply
my project is Sol gel process how to prepare this process pls tell me
the dimension of work and energy is ML2T2 find the unit of work and energy hence drive for work?
Emmanuel Reply
Two bodies P and Quarter each of mass 1000g. Moved in the same direction with speed of 10m/s and 20m/s respectively. Calculate the impulse of P and Q obeying newton's 3rd law of motion
Shimolla Reply
the answer is 0.03n according to the 3rd law of motion if the are in same direction meaning they interact each other.
definition for wave?
Doc Reply
A disturbance that travel from one medium to another and without causing permanent change to its displacement
In physics, a wave is a disturbance that transfers energy through matter or space, with little or no associated mass transport (Mass transfer). ... There are two main types ofwaves: mechanical and electromagnetic. Mechanicalwaves propagate through a physical matter, whose substance is being deformed
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Note: LINEAR MOMENTUM Linear momentum is defined as the product of a system’s mass multiplied by its velocity: size 12{p=mv} {}
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Study of matter and energy
physics is the science of matter and energy and their interactions
physics is the technology behind air and matter
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Easy to learn
31. Calculate the initial (from rest) acceleration of a proton in a 5.00×106 N/C electric field (such as created by a research Van de Graaff). Explicitly show how you follow the steps in the Problem-Solving Strategy for electrostatics.
Catina Reply
A tennis ball is projected at an angle and attains a range of 78. if the velocity is 30metres per second, calculate the angle
what friction
Wisdom Reply
question on friction
the rubbing of one object or surface against another.
momentum is the product of mass and it's velocity.
what are bioelements?
Friction is a force that exist between two objects in contact. e.g. friction between road and car tires.
Practice Key Terms 7

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