**Force**

**We know about Acceleration ...**

Power

**Force, Work, and Power**

The 'Power' pyramid has 'Work' in the top block as well.

**... and we know about distance**

**But, what about ... FORCE!**

acc. =

Units of acceleration are ...

m/s

f - i

________

t

Distance

- generally measured in meters (m)

- go back to the metric unit to review conversions ...

- to convert to meters from other untis

Delta Force

I'm gonna force you to make a decision

The force of his will was too strong

Force out at first base

**But, what is force in science?**

V

V

2

Force

equals mass

times acceleration

F

=

m

a

so.......

F

m

a

... and ...

The units of force are ...

Newton's

(N)

... yes, after Sir Isaac

Now do the Force reading assignment

... at the completion of it, you should be able to work the Force problems assignment.

THEN.... you are ready to move on to ....

... is a four letter word,

to some people.

But ....

... to a physics guy, it is ...

A measure of the transfer of

energy in a system.

Work

Equals

Force

Times

Distance

or ....

W

F

d

And ...

the units for Work are ...

Joules (J)

You push a box with 50 N of force, it moves 2.5 m. So....

W = F * d

W = 50 N X 2.5 m

W = 125 J

Let's try another

5,000 J of work are done to lift a load 25 m into the air. How much force is applied?

F = W /d

so...

F = 5,000 J / 25m

F=

200 N

...And another.

A crane does 25,000 J of work lifting a box with 5,100 N of force.

How far does it go?

d =

W / F

d =

25,000 J

5,100 N

d =

4.9 m

You should now be ready to do the

Work portion of the assignments ...

Do those now ....

Then come back to review the lesson on power.

Is a measure of how FAST work is done.

The faster it is performed,

the more power is generated.

The more work is done,

the more power is generated.

w

P

t

A sprinter does 1,250 J of work to fly out of the starting blocks. She does this in 5 seconds. How much power does she generate?

P

=

w

/

t

so ...

P

=

1,250 J

/

5s

P

=

250 W

A few points to be aware of...

1) The units for Power are Watts (W)

-CAPITAL W!

2) The symbol for Work is (w)

- lower case w!

I know this is confusing ...

...you just have to deal with it, sorry.

So, let's try a few...

An electric pulley generates 575 W of power while pulling a load in 12.5 seconds. How much work is done?

w

=

P X t

so ...

w =

575 W

X

12.5 s

w =

7187.5

J

And another ...

And yet another ...

An electric motor runs a saw blade. It generates 700 W of Power, while doing 4,900 J of work. How long does this take?

t =

w

/

P

so ...

t =

700 W

/

4,900 J

t =

7

s

You should now be able to complete the Power portion of the Work and Power assignments ...

Then ...

... you will be able to take the ...

F, W and P Party, yahoo!!!

A block has mass of 55 kg. It is accelerated at a rate of 2.5 m/s. How much force is used?

2

F =

m X a

F =

55 kg X 2. 5 m/s

2

F =

137.5

N

Now you try a few ...

How much force is required to accelerate a 45 kg Ice skater at 3.85 m/s ?

2

A 50 kg crate is lifted with an acceleration of 8.5 m/s . How much force is used?

2

**Here you will learn how to solve for all variables for all three quantities.**