The net force is defined as the sum of all the forces acting on an object. An example? When you kick a soccer ball, the ball takes off and moves through the air. At that moment, there is a net force acting on the ball. When the ball begins to return to the ground and finally stops, there is a net force acting on the ball as well.
Newton's Second Law says that "when a net force acts on an object, then that object must accelerate, that is, its speed changes from second to second." When you kick the soccer ball for the first time, it accelerates, and when the soccer ball begins to brake to a stop, it is also accelerating.
There can be several forces acting on an object, and when all those forces are added together, the result is what we call the net force acting on the object.
If the net force adds to zero, then the object is not accelerating, therefore it is moving with a constant velocity. If the net force is added to a nonzero value, then the object is accelerating.
In nature, all forces oppose other forces, such as friction or opposing gravitational forces. Forces can only produce acceleration if they are greater than the total opposing forces.
If a force pushes an object, but is coupled by friction, the object does not accelerate. Similarly, if a force pushes against gravity but is less than the gravitational force on an object, it does not accelerate.
For example, if a 15-Newton push on an object is opposed by a 10-Newton friction force, the object accelerates as if it were pushed by a frictionless 5-Newton net force.
Second law of Newton
Newton's first law of motion predicts the behavior of objects for which all existing forces are balanced.
The first law, (sometimes called the law of inertia) states that if the forces acting on an object are balanced, then the acceleration of that object will be 0 m / s / s. Objects in equilibrium (the condition in which all forces balance out) will not accelerate.
According to Newton, an object will only accelerate if there is a net or unbalanced force acting on it. The presence of an unbalanced force will accelerate an object, changing its speed, its direction, or its speed and direction.
Newton's second law of motion
This law refers to the behavior of objects for which not all existing forces are balanced. The second law states that the acceleration of an object depends on two variables: the net force acting on the object and the object's mass.
The acceleration of an object depends directly on the net force acting on the object, and inversely on the mass of the object. As the force acting on an object increases, the acceleration of the object increases.
As the mass of an object increases, the acceleration of the object decreases. Newton's second law of motion can be formally stated as follows:
"The acceleration of an object produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force and inversely proportional to the mass of the object."
This verbal statement can be expressed in the form of an equation as follows:
A = Fnet / m
The above equation is often rearranged to a more familiar form as shown below. The net force is equated to the product of the mass multiplied by the acceleration.
Fnet = m • a
The emphasis is always on net force. Acceleration is directly proportional to net force. Net force equals mass times acceleration.
Acceleration in the same direction as the net force is an acceleration produced by a net force. It is the net force that is related to the acceleration, the net force is the vector sum of all the forces.
If all the individual forces acting on an object are known, then the net force can be determined.
According to the equation above, a unit of force is equal to a unit of mass multiplied by a unit of acceleration.
By substituting standard metric units for force, mass, and acceleration in the above equation, the following unit equivalency can be written.
1 Newton = 1 kg • m / s2
The definition of the standard metric unit of force is indicated by the above equation. One Newton is defined as the amount of force required to give a mass of 1 kg and an acceleration of 1 m / s / s.
Magnitude and equation
According to Newton's Second Law, when an object is accelerated, then there must be a net force acting on it. Conversely, if a net force acts on an object, that object will accelerate.
The magnitude of the net force acting on an object is equal to the mass of the object multiplied by the acceleration of the object as shown in the following formula:
A net force is the remaining force produced by any acceleration of an object when all opposing forces have been canceled.
Opposing forces decrease the effect of acceleration, decreasing the net force of acceleration acting on an object.
If the net force acting on an object is zero, then the object is not accelerating and is in a state we call equilibrium.
When an object is in equilibrium, then two things can be true: either the object is not moving at all, or the object is moving with a constant speed. The formula for equilibrium is shown below:
Examples
Let's consider a hypothetical situation in space. You are doing a spacewalk and fixing something on your shuttle. While working on the subject with a wrench, she gets angry and throws the wrench away, what happens?
Once the key leaves the hand it will continue to move with the same speed that it gave when you released it. This is an example of a zero net force situation. The key will move with the same speed and will not accelerate in space.
If you throw the same key on Earth, the key will fall to the ground and eventually stop. Why did it stop? There is a net force acting on the key, causing it to slow down and stop.
In another example, let's say you are on an ice rink. Take a hockey puck and slide it across the ice.
Eventually the hockey puck will slow down and stop, even on smooth, slippery ice. This is another example of a situation with a nonzero net force.
References
- The Physics Classroom,. (2016). Newton's Second Law. 11-2-2017, from physicsclassroom.com Website: physicsclassroom.com.
- Cárdenas, R. (2014). What is Net Force? - Definition, Magnitude & Equations. 11-2-2017, from http://study.com Website: study.com.
- IAC Publishing, LLC. (2017). What is net force ?. 11-2-2017, from Reference.com Website: reference.com.
- Net force. (nd) Webster's Revised Unabridged Dictionary. (1913). Retrieved February 11 2017 from thefreedictionary.com.
- Pearson, A. (2008). Force and Motion Chapter 5. Force and Motion. 2-11-2017, from Pearson Education Inc Website: physics.gsu.edu.