# Newton's second law review (article) | Khan Academy (2023)

## Want to join the conversation?

• Elan Fayngersh

4 years agoPosted 4 years ago. Direct link to Elan Fayngersh's post “The videos on Newton Seco...”

The videos on Newton Second Law of Motion only showed things in their current state; how would you show something moving, for example, accelerating North at 20 Newtons and slowing down by a Southern moving force of 15 Newtons. How would that be shown in an illustration like the ones in the video?

• Fiona T

2 years agoPosted 2 years ago. Direct link to Fiona T's post “If you wanted to illustra...”

If you wanted to illustrate the object in a free body diagram, you would just draw the forces acting on it, as in the example you gave with 20N north and 15N south (similarly to how the objects were shown in the video). The object's velocity and acceleration are not included as part of a free body diagram, but I usually notate those as arrows on the side for visual convenience.

• Davïd

a year agoPosted a year ago. Direct link to Davïd's post “This is some yummy brain ...”

This is some yummy brain food!
Nom nOm noM.

(Video) Newton's second law of motion | Forces and Newton's laws of motion | Physics | Khan Academy
• Danlearning

3 years agoPosted 3 years ago. Direct link to Danlearning's post “Hi! I'm wondering why the...”

Hi! I'm wondering why the velocity could be non-zero when the forces are at equilibrium (F_net=0) and when the acceleration is also 0. Shouldn't velocity only be 0 (according to Newton's First Law) because the forces are balanced and acceleration doesn't exist?

• BeeGee

3 years agoPosted 3 years ago. Direct link to BeeGee's post “Okay, I'm going to remind...”

Okay, I'm going to remind you of some things you already know: acceleration can be defined as the change in velocity over time, and if a force is being applied to something it should accelerate unless an equal and opposite force is being applied. (An equal force is being applied in the direction opposite of the original force)
If an object is moving, and there are no forces being applied to is (no friction, gravity, or any work whatsoever) then it is not accelerating, as a force is necessary for acceleration to be observed, and at the same time there are no forces, so F_net=0.
Okay, you say, but what if there are forces?
The same principle- as you know F_net=F_1+F_2+...+F_n, so if I were pushing a box along a plane with friction, applying a force of 10 N, and the friction on the box was 10 N in the opposite direction, we would say that the net force is zero, F_net=0, which means there is ALSO no acceleration, even though the box is moving, which means there is a velocity.

• Rukaiya

4 years agoPosted 4 years ago. Direct link to Rukaiya's post “Is it possible a body can...”

Is it possible a body can be in motion without any force?

• itpc932874

4 years agoPosted 4 years ago. Direct link to itpc932874's post “If it is moving at a cons...”

If it is moving at a constant velocity, there are not any net forces.

(1 vote)

(Video) Newton's Second Law of Motion
• Salam Lababidi

2 years agoPosted 2 years ago. Direct link to Salam Lababidi's post “hello, please I would lik...”

hello, please I would like to know when is the acceleration considered to be negative?

(1 vote)

• IsotonicFlaccidCell21

2 years agoPosted 2 years ago. Direct link to IsotonicFlaccidCell21's post “When your velocity starts...”

When your velocity starts to decrease, for example when a car is coming to a halt just before a traffic light (Retardation).

• 1khaldiwafa

(Video) Rotational version of Newton's second law | Physics | Khan Academy

3 years agoPosted 3 years ago. Direct link to 1khaldiwafa's post “EquilibriumThe forces ar...”

EquilibriumThe forces are balanced, so net F equals 0 and the system is not accelerating. Velocity can be non-zero. i have not really undrstood the state of the velocity.

• aqeelah1995

2 years agoPosted 2 years ago. Direct link to aqeelah1995's post “Can you cover the topic o...”

Can you cover the topic of balancing objects or equilibrium?

• iceberg

2 years agoPosted 2 years ago. Direct link to iceberg's post “I don't understand exactl...”

I don't understand exactly how an object with constant velocity that isn't at rest has a resultant force of zero, is there always some kind of opposing force? But what if there isn't a force such as friction or air resistance? I'm confused

(1 vote)

• pa_u_los

2 years agoPosted 2 years ago. Direct link to pa_u_los's post “Acceleration implies forc...”

Acceleration implies force. If we have constant velocity that means that we don't have acceleration. If we don't have an acceleration, that means that there's no force involved.

In real life, yes. If we only focus on classical mechanics and not the physics behind it that explains more profoundly why it works like that, I can't think of any force that doesn't have an opposing force. Every material has an associate coefficient of friction. If there's no force such as friction or air resistance, objects would experience a constant acceleration, meaning they would be speeding up until reaching the speed of light all the time. Because if we are at a rest (0 velocity) and want to change our velocity we need a force. And that force wouldn't had a counterpart. We would be constantly accelerating, making life pretty difficult. If not, not viable.

(Video) AP Physics 1 review of Forces and Newton's Laws | Physics | Khan Academy
• Zoe LeVell

2 years agoPosted 2 years ago. Direct link to Zoe LeVell's post “If the sum of the forces ...”

If the sum of the forces and acceleration always point in the same direction, but forces can never be negative, then how can acceleration be negative?

(1 vote)

• IsotonicFlaccidCell21

2 years agoPosted 2 years ago. Direct link to IsotonicFlaccidCell21's post “Forces can be negative. F...”

Forces can be negative. Forces are vectors. Here is an example:
you are pushing a box with a force of 5N. However, friction with the ground is pushing bat with a force of 2N. Hence, if you were to add all the forces it would be 5 + (-2) =3. This is because the 2N is acting in the opposite direction, hence it is negative.
For your second part (how acceleration can be negative):
let's say you are at terminal velocity (Constant velocity) in the air and you are falling. Your weight is (let's say) 700N. You suddenly open up your parachute, causing air resistance, pushing you up with a force of 1000N. As going down is a positive force, the resultant force would be 700 + (-1000) = -300N. Here you have a negative force going downwards, meaning that you are decelerating (retarding). This is how acceleration is negative. As the force is negative, and your mass is constant and positive, that means your acceleration downwards must be negative. Thus you will slow down.

(1 vote)

• NolanW

17 days agoPosted 17 days ago. Direct link to NolanW's post “I have forgotten how to d...”

I have forgotten how to do Newton's second and first laws I NEED HELP I HAVE A QUIZ ON FRIDAY PLEASE ANYONE HELP ME!

(1 vote)

## FAQs

### What is Newton's 2nd law Review? ›

Newton's second law says that the acceleration and net external force are directly proportional, and there is an inversely proportional relationship between acceleration and mass.

What is the second law of Newton Khan Academy? ›

Newton's second law of motion is F = ma, or force is equal to mass times acceleration.

What is Newton's 2nd law article? ›

Newton's second law is a quantitative description of the changes that a force can produce on the motion of a body. It states that the time rate of change of the momentum of a body is equal in both magnitude and direction to the force imposed on it.

What is Openstax Newton's second law? ›

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. a = F net m .

Why is Newton's second law the most important? ›

It's used in almost every chapter of every physics textbook, so it's important to master this law as soon as possible. We know objects can only accelerate if there are forces on the object. Newton's second law tells us exactly how much an object will accelerate for a given net force.

What are 2 examples of Newton's second law? ›

The Most Common Applications of Newton's Second Law of Motion
• 1· Try to move an object.
• 2· Pushing a car and a truck.
• 3· Racing Cars.
• 4· Rocket launch.
• 5· Kick the ball.
• 6· Car crash.
• 7· Two people walking.
• 8· Object thrown from a height.
Nov 15, 2021

How is Newton's 2nd law applied? ›

The acceleration of an object depends directly upon the net force acting upon the object, and inversely upon the mass of the object. As the force acting upon an object is increased, the acceleration of the object is increased. As the mass of an object is increased, the acceleration of the object is decreased.

When was Newton's 2nd Law discovered? ›

Isaac Newton's laws of motion were first set down in his Principia Mathematica Philosophiae Naturalis in 1687.

What are the two consequences of Newton's second law of motion? ›

1 It shows that the motion is accelerated only when force is applied. 2 It gives us the concept of inertial mass of a body.

How does second law of motion help us measuring of force? ›

According to Newton's second law of motion, force is directly proportional to the rate of change of momentum.

### What Newton's law is Openstax? ›

Newton's First Law of Motion. A body at rest remains at rest or, if in motion, remains in motion at constant velocity unless acted on by a net external force. Note the repeated use of the verb “remains.” We can think of this law as preserving the status quo of motion.

What is Newton's second law chegg? ›

Newton's second law states that the rate of change of momentum of an object is directly proportional to the force applied. The change in momentum is in the direction of the force applied.

How does Newton's second law relate to everyday life? ›

Newton's Second Law of Motion says that acceleration (gaining speed) happens when a force acts on a mass (object). Riding your bicycle is a good example of this law of motion at work. Your bicycle is the mass. Your leg muscles pushing pushing on the pedals of your bicycle is the force.

What is another name for Newton's 2nd law? ›

According to Newton s Second Law of Motion, also known as the Law of Force and Acceleration, a force upon an object causes it to accelerate according to the formula net force = mass x acceleration.

What does Newton's second law explain quizlet? ›

Newton's second law states that the acceleration produced by a net force on an object is directly proportioned to the magnitude of the net force, is in the same direction of the net force, and is inversely proportioned to the mass of the object.

What is Newton's second law KIDS definition? ›

The second law states that the greater the mass of an object, the more force it will take to accelerate the object. There is even an equation that says Force = mass x acceleration or F=ma. This also means that the harder you kick a ball the farther it will go.

Which is the Newton's law best explain? ›

The idea that objects only change their velocity due to a force is encapsulated in Newton's first law. Newton's first law: An object at rest remains at rest, or if in motion, remains in motion at a constant velocity unless acted on by a net external force.

Why Newton's second law is called? ›

Newton's second law of motion is called a law of momentum. It states that the acceleration produced in an object due to applied net force on it is directly proportional to the magnitude of the force. Newton's third law of motion is called a law of action-reaction.

## Videos

1. Math Review for Newton's Second Law
(Kenneth Miller)
2. Newton's Second Law of Motion - Force, Mass, & Acceleration
(The Organic Chemistry Tutor)
3. Newton's Second Law of Motion: F = ma
(Professor Dave Explains)
4. Normal force in an elevator | Forces and Newton's laws of motion | Physics | Khan Academy
5. Newton's Second Law
(The Physics Classroom)
6. Newton's second law - Problem
(Everest Physics)
Top Articles
Latest Posts
Article information

Author: Allyn Kozey

Last Updated: 03/21/2023

Views: 5671

Rating: 4.2 / 5 (63 voted)

Author information

Name: Allyn Kozey

Birthday: 1993-12-21

Address: Suite 454 40343 Larson Union, Port Melia, TX 16164

Phone: +2456904400762