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Force and Work
TEKS:
6.8B – IDENTIFY AND DESCRIBE THE CHANGES IN POSITION, DIRECTION AND SPEED OF AN OBJECT WHEN ACTED UPON BY UNBALANCED FORCES
7.7A – CONTRAST S ITUATIONS WHERE WORK IS DONE WITH DIFFERENT AMOUNTS OF FORCE TO S ITUATIONS WHERE NO WORK IS DONE SUCH AS MOVING A BOX W ITH A RAMP AND WITHOUT A RAMP, OR STANDING STILL
Concept Map Time!I need a volunteer to start us off on the white board!
Force
Work
Types of
forces
Gravity
Motion
Take a picture of the concept map if you wish – we will add to a more formal version later!
Anticipation GuideFollow directions on the page, when done, place it in your binder. This goes in front of your notes we are about to take!
FIB Notes page:
Vocabulary to know:
Force – a push or pull
Energy – is the ability to do work.
Work – is the result of force moving an object (or the transfer of energy to that object)
Effort – The force you apply to a simple machine.
Load – the object being moved
Simple Machine – devices that reduce the amount of work needed to move an object.
What is a Force?
More specific definition: A force is a push or pull that causes an object to move, stop, or change direction
Balanced and Unbalanced ForcesLet’s learn how forces work.
Balanced Forces
1. Balanced forces do not cause change in motion
2. They are equal in size and opposite in direction
Balanced Forces
Examples of balanced forces:
Unbalanced Forces1. An unbalanced force always causes a change in motion
When forces act, you can find the net force
2. Net force is the overall force acting on an object. It is a combination of the magnitude and the direction.
a. MagnitudeThe size of the forces
b. DirectionDirection of the largest force
Examples of Unbalanced Forces
The soccer ball doesn’t move until the girl provides an unbalanced force upon it.
The tug of war doesn’t have the same amount of people on each side, so the forces are unequal and the rope will move toward the side with more people
How to calculate net forceOnce again - the net force is the overall force or total amount of force acting on an object (a combination of the magnitude and direction) If the forces are going in opposite directions:
For example, in this tug of war, the net force is 2N to the right
The forces are in
opposite
directions.
Subtract the
numbers.
How to calculate net forceIf the forces are going in the same direction, you add the overall forces.
For example, in this tug of war, the net force is 250N to the right
The forces are in the
same direction.
Add the numbers.
How are force and work related?Again, work means that a force (your effort) was used in order to move an object
You know that work has been done if a force makes an object move some distance.
This man lift the table up (distance), so work must have been done on it
Examples of no work being done:
No work without motion ◦ If the object didn’t move (it didn’t travel a distance), then no work occurred
Men are pushing with equal force –
Box doesn’t move
Barbell doesn’t move
(he’s just holding it)
Examples of WORK being done:
The force applied to this box makes
it travel a certain distance. When
the box moves, work is being done
The force applied to the pulley
makes the load travel a certain
distance. When the load moves up,
work is being done
Check for understanding: Is work being done?
Standing still - when you are standing still, the is no movement nor change in direction, so no work is occurring
Check for understanding:Is work being done?
Box moved without a ramp Box moved with a ramp
Tip: ask yourself, “Is a force being used to move an object (a distance)?”
The end result – the amount of work being done is the same. Simple machines just help
us do the work!
Calculating WorkFormula for Work:
Work = force x distance or W = f x d
The formula with units included:
Work (J) = force (N) x distance (m)
In science, every number has a unit!
Unit for force: Newtons (N)
Unit for distance: meters (m)
Units for work – joules (J)
A practice problem:
Calculate the amount of work done when moving a 5N crate a distance of 20 meters.
W = F x DW = 5N x 20mW = ?
Work done is = 100 J
Must include units!
Write this example down!
Your notes should be complete now.
Where do you put them?
HW – due next class (if not done in class):Start NOW and complete at home:
