Introduction to Force in Physics
Now let's talk about Force.
On several previous lectures, I mentioned it frequently.
It's a very important physical quantity.
Yes, it's a kind of physical quantity.
In physics, Force is vector physical quantity.
Force has magnitude and direction.
Please study vector calculate through below links. Vector calculations are very important in science.
http://www.mathsisfun.com/algebra/vectors.html
http://www.mathsisfun.com/algebra/vectors-dot-product.html
http://www.mathsisfun.com/algebra/vectors-cross-product.html
Force makes some changes for the status of an object.
Because of force, something can be broken. The shape of an object might be changed.
We can imagine the phenomena due to force.
But in physics, the definition of force is a little unique.
I will express it by mathematics.
F = ma
Force is mass times acceleration.
Consequently force is related with acceleration.
And fore is the source of acceleration. Where there is acceleration there is force generating it. And because of acceleration, an object with having acceleration has the change of velocity with respect to time.
Someone can ask something like that what is the origin of force.
I won't tell you now for it.
Think about it. It's a very interesting issue.
However instead of arguing the issue, we can say that to generate force we need energy. Later we will access to physical phenomena with using energy conception. It's also exciting concept. Meanwhile please be patient.
Let's think about the first theme on the below link.
http://physicswith.blogspot.com/2015/05/motion-in-one-dimension.html
By stepping an accelerator the car was faster gradually.
With that action, the car got force so that it has acceleration.
By that action, the engine of the car generates force to give to the car.
In the engine gasoline exploded and fuel energy changes into mechanical energy.
With the energy, it gives force to the car continuously as long as he is stepping the accelerator pedal.
Through the definition of force, what is the force affecting to the car?
F = ma -> 100 * 1 = 100 kg m/s2.
Force is a vector. The magnitude is 100 kg m/s2, and the direction is (+) direction.
It has its own physical unit. As we can see above, the unit is kg*m/s2. Or N. We call "N" newton that is from Issac Newton, the great scientist.
( N ) = ( kg*m/s2)
So the car has 100 N force toward right direction.
And this force is being generated by the car's engine.
I will make a new situation for the car.
In this time there is a frictional force between the car and the surface of the straight road.
force1
Frictional force is also interesting one. Think about it, what is the origin of frictional force between 2 objects.
Anyway frictional force bothers movement of objects.
It is vector physical quantity too. It has proper magnitude and direction.
The main property of frictional force is that its direction is always opposite with the direction of velocity.
I will set frictional force by Ff. The direction is (-), left, so Ff = (-) 20 N.
And car's engine force by Fe. Fe = (+) 100 N.
So consequently the car has (+) 80 N force. The direction is right.
We call this force which is calculated through two vectors, Ff + Fe, "net force".
I will set net force by Fn. So Fn = (+) 80 N.
Then what is the acceleration of the car in this case?
We should remind of motion equation mathematically.
Fn = ma -> (+) 80 = 200 * a -> a = 80/200
Because of frictional force, the acceleration becomes smaller. However anyway it's just constant acceleration motion.
Then,
HW1) How long will it take to pass by his home?
And What is the velocity at that time?
HW 2)
Now, there is another force on the car. It's air resistance force. I will set it by Fa.
And Fa = (-) 20N . As you know, Fa interrupts the car's movement.
Then What is the acceleration of the car?
HW 3)
And Morover, wind is blowing toward left direction continuously. It's strong wind. The force of wind is providing 80 N to the car. So the force of wind is denoted by Fw, Fw = (-) 80 (N).
Assume that the car can generate only 100 N force by its engine continuously.
(1) Find out the car's acceleration. And forcast its motion.
(2) Draw a graph for velcity with repect to time. And describe the car's motion by the graph.
(3) Draw a graph for displacement with respect to time.
(4) Draw a graph for distance of the car with respect to time.
(5) He will be able to reach his home?
On several previous lectures, I mentioned it frequently.
It's a very important physical quantity.
Yes, it's a kind of physical quantity.
In physics, Force is vector physical quantity.
Force has magnitude and direction.
Please study vector calculate through below links. Vector calculations are very important in science.
http://www.mathsisfun.com/algebra/vectors.html
http://www.mathsisfun.com/algebra/vectors-dot-product.html
http://www.mathsisfun.com/algebra/vectors-cross-product.html
Force makes some changes for the status of an object.
Because of force, something can be broken. The shape of an object might be changed.
We can imagine the phenomena due to force.
But in physics, the definition of force is a little unique.
I will express it by mathematics.
F = ma
Force is mass times acceleration.
Consequently force is related with acceleration.
And fore is the source of acceleration. Where there is acceleration there is force generating it. And because of acceleration, an object with having acceleration has the change of velocity with respect to time.
Someone can ask something like that what is the origin of force.
I won't tell you now for it.
Think about it. It's a very interesting issue.
However instead of arguing the issue, we can say that to generate force we need energy. Later we will access to physical phenomena with using energy conception. It's also exciting concept. Meanwhile please be patient.
Let's think about the first theme on the below link.
http://physicswith.blogspot.com/2015/05/motion-in-one-dimension.html
By stepping an accelerator the car was faster gradually.
With that action, the car got force so that it has acceleration.
By that action, the engine of the car generates force to give to the car.
In the engine gasoline exploded and fuel energy changes into mechanical energy.
With the energy, it gives force to the car continuously as long as he is stepping the accelerator pedal.
Through the definition of force, what is the force affecting to the car?
F = ma -> 100 * 1 = 100 kg m/s2.
Force is a vector. The magnitude is 100 kg m/s2, and the direction is (+) direction.
It has its own physical unit. As we can see above, the unit is kg*m/s2. Or N. We call "N" newton that is from Issac Newton, the great scientist.
( N ) = ( kg*m/s2)
So the car has 100 N force toward right direction.
And this force is being generated by the car's engine.
I will make a new situation for the car.
In this time there is a frictional force between the car and the surface of the straight road.
force1
Frictional force is also interesting one. Think about it, what is the origin of frictional force between 2 objects.
Anyway frictional force bothers movement of objects.
It is vector physical quantity too. It has proper magnitude and direction.
The main property of frictional force is that its direction is always opposite with the direction of velocity.
I will set frictional force by Ff. The direction is (-), left, so Ff = (-) 20 N.
And car's engine force by Fe. Fe = (+) 100 N.
So consequently the car has (+) 80 N force. The direction is right.
We call this force which is calculated through two vectors, Ff + Fe, "net force".
I will set net force by Fn. So Fn = (+) 80 N.
Then what is the acceleration of the car in this case?
We should remind of motion equation mathematically.
Fn = ma -> (+) 80 = 200 * a -> a = 80/200
Because of frictional force, the acceleration becomes smaller. However anyway it's just constant acceleration motion.
Then,
HW1) How long will it take to pass by his home?
And What is the velocity at that time?
HW 2)
Now, there is another force on the car. It's air resistance force. I will set it by Fa.
And Fa = (-) 20N . As you know, Fa interrupts the car's movement.
Then What is the acceleration of the car?
HW 3)
And Morover, wind is blowing toward left direction continuously. It's strong wind. The force of wind is providing 80 N to the car. So the force of wind is denoted by Fw, Fw = (-) 80 (N).
Assume that the car can generate only 100 N force by its engine continuously.
(1) Find out the car's acceleration. And forcast its motion.
(2) Draw a graph for velcity with repect to time. And describe the car's motion by the graph.
(3) Draw a graph for displacement with respect to time.
(4) Draw a graph for distance of the car with respect to time.
(5) He will be able to reach his home?
