Good morning. Today, we are going to define and show examples of Force.
Hey guys. Hey Bo. H-hi Bo.
A force is a
-a push or a pull!
Actually no Billy. I don't like to define a force as a push for a pull because it's not really clear
what a force is then.
And please raise your hand if you have a question or a comment
I'm sorry, Mr. P
Billy, it's okay. A force is the ability to cause a change in state of motion of an object
And you should know that force,
mass and acceleration are all related.
Force is the ability to cause a change in state of motion of an object. A change in state of motion is an
acceleration and mass is a measurement of the tendency of an object to resist acceleration.
So again force, mass and acceleration are all related. Let's do a demonstration of this concept.
Above me is a block.
That block is tied to a string. That string goes over a pulley and is attached to a mass hanger.
Now, that mass hanging will apply a force to the block and as you can see, it will accelerate the block.
Billy, what will happen if we add mass to the mass hanger which will increase the force applied to the block?
What will it do to the acceleration of the block?
An increase in force should increase the ability to cause acceleration and so the acceleration should go up
Correct Billy. You can see that with more mass on the mass hanging
and therefore an increase to the force applied to the block,
the block's acceleration increases.
Now Bo, what do you think will happen to the acceleration of the block if I keep the force applied the same
however, I place mass on top of the block and therefore increase the mass of the block?
Increasing the mass of the block should increase the resistance to a change in state of motion of the block
And therefore should decrease the acceleration of the block.
You are correct.
You can see that when the mass of the block is increased, the resistance to acceleration is increased
and therefore, with the same force applied, the acceleration of the block will decrease.
Now, I want to take a moment to highlight a part of the definiti on of force we have yet to talk about.
A force is the ability to cause a change in state of motion of an object.
In other words, the presence of a force doesn't necessarily mean
there will be a change in state of motion of the object.
Watch what happens when I place a large mass on the block.
Now the force applied by the mass hanging is unable to cause a change in state of motion of the block.
Billy, why not?
Because the block has too much
mass or too much tendency to resist a change in state of motion
and there isn't enough force to overcome that resistance.
I'm sorry Billy. That's not correct.
When we get the block to not accelerate.
It is being pressed into the table hard enough
that the force of friction is strong enough
to balance out the force pulling it to the left
The challenge is that when we increase the inertia of the block by increasing its mass,
we also increase how much force is pressing the block against the table.
It is easy to think more inertia always means there is a new minimum force necessary to accelerate it.
However that is not true.
Usually when you are thinking about a minimum force being needed, it is because of the force of friction.
Never just because of having too much mass. In other words too much inertia.
We will talk more about the way the force of friction works in future lessons.
At this point simply know that too much mass will never cause an object not to accelerate.
*ACHOO*
Bless you! What happens if you increase the force applied?
Okay Bo, let's find out.
You can see I increased the force applied enough to overcome the force of friction
which was increased by the increased block mass.
Again, we have yet to define force of friction, but we will. Please be patient.
Man! I hate being patient.
I know let's go back to the whiteboard
Force is a vector
which means, class, it has both...?
Magnitude and Direction!
Please remember that force is a vector and therefore, has both magnitude and direction.
Also know that a force is always the result of an interaction between two objects.
For example, when I fall out of this tree
the force of gravity is the result of an interaction between my body and the Earth.
When this car slides to a stop,
the friction force is the result of an interaction between the tires and the ground.
And when this sled lands on the ground,
the force applied is the result of the interaction between the sled and the ground.
And finally, two different categories of forces:
Contact Force and Field Force
With a Contact Force, the two interacting objects will touch one another
and in a Field Force, the two interacting objects
do not have to touch one another
So the examples of Contact Forces are the Applied Force, the Drag Force, the force of friction
The Force Normal, the Force caused by a spring and the Tension Force.
And we will define them just not today
Some examples of field forces are the force of gravity which is also called weight,
the Magnetic Force and the Electric Force.
The Force of Gravity is probably the one you're most familiar with.
Going back to the example where I fall out of the tree: That force of gravity, my weight, is a field force.
Now, it's an interaction between the Earth and me and
the Earth is not touching me while I'm falling toward the Earth however the Earth is still pulling me down and
applying a Force of Gravity on me and
after I land, the force of gravity is still a field force even though the earth and I are touching one another.
A Field Force is sometimes called an action-at-a-distance force because
the two objects that are interacting and causing this force can have a distance between the two of them
Thank you very much for learning with me today. I enjoyed learning with you.
*FACEPLANT*