1. Elastic-Normal-Friction
Forces
Elastic-Normal-Friction

2. SPRINGS Why did we make a line of best fit for our data?
Here’s our slope- what does it tell us about the red spring?
2nd = 3.737cm/N 3rd = cm/N 4th= cm/N
6th= cm/N 7th= cm/N
When finding the slope, why do we choose the “circled” points to calculate it?
What does this slope tell you about this spring?
How much weight is hanging on the spring if it stretches 23.7 cm?

3. Robert Hooke’s finding
F = k Dx
F is the force applied
x = the change in length of the spring
k = a spring constant (usually expressed in N/cm)
k depends on what it is made of, temperature thickness of the material etc.
What does this mean? Force & change in spring length are PROPORTIONAL
If you know k, you can predict x when a particular force is applied- like on bridges!

4. Elastic Materials Hooke’s Law applies to all elastic materials-
This means that all elastic materials have a linear graph like what we got for the red spring.
* What if we had a spring that was thinner than the red spring.
What would it’s graph look like?
* What if it were a thicker, more tightly coiled spring, what would it’s graph look like?

5. Draw a model of an atom & identify its 3 main parts with their charges

6. Which objects will apply an ELASTIC FORCE?
Clay
Rubber stopper
Coal
Popsicle stick
String
Spring
Rubber band

7. Will this linear graph go on forever?
change in length vs Fg
What makes springs elastic?
Change in spring length (cm)
Fg (N)

8. The Big Spring Elastic Phase- can go back to its original shape
Plastic Phase- is deformed & can’t go back to its original shape
Breaking Point- is broken apart

9. The spring
Press on spring between finger/thumb & keep spring still & in elastic phase
Did the spring push back?
How hard?
F push = F el
Would the same be true if it were a balloon or a dodgeball or a sponge?
Now press a bit harder on the spring
Does the spring still push back?
How does it know to push back harder (copy your push)?

10. How MATTER is arranged All matter is made of atoms & molecules
Atoms & molecules in solids are arranged & bonded in a pattern (magnet demo)
Bonds between atoms
are electromagnetic field forces
that hold them together in
their pattern.

11. Why do things stretch and break?
Solid being pulled
Molecules in a solid
Atoms/molecules get pushed/pulled out of their pattern in the solid, if they can find their way back to their original spot- they are in the elastic phase
*What happens in the plastic phase?
*What happens when they break?

12. How does the spring know to push back more (copy your push)?
The atoms want to go back to their original spot.
The more you push, the more they push back because you are making them too “crowded”.
That’s better! Now I’m not so crowded!
Stop repelling & pushing on me!

13. What is the name of the force from the spring pushing on your finger?
ELASTIC FORCE
Push or pull from solids that are stretchy or springy
Where does that elastic force come from?

14. Stapler on table Is stapler pushing on the table? What direction?
How can we measure it? DO IT!
Name that force
Is table pushing back?
How much?
Will the table push on all things with that same number of Newtons?

15. How does the table know how hard to push up on the stapler?
See model
The NORMAL FORCE is from the atoms being pushed but they still stay in their pattern
The atoms are repelling each other because they are too close- the closer they get, the more they repel & push back
FN = Fw

16. NORMAL/SUPPORT FORCE What if we set the stapler on tissue?
*WHY did that happen?
The bonds between the tissue atoms are too weak- they can’t push back with enough Newtons so the stapler’s weight force rips them out of their place & the stapler falls
The bonds between atoms in the tissue can’t support the stapler.

17. WHY IS IT NORMAL?
Normal is a math term for PERPENDICULAR (at 90o angle)
The normal force is a push from a HARD SURFACE and always pushes in the direction PERPENDICULAR to the surface of the agent

18. Which force is it? Name that force

19. How MATTER is arranged All matter is made of atoms & molecules
Atoms & molecules in solids are arranged & bonded in a pattern (magnet demo)
Bonds between atoms
are electromagnetic field forces
that hold them together in
their pattern.
Surfaces of solids look smooth
but they are really bumpy at the
microscopic level.

20. Smooth solids are bumpy when magnified
steel

21. Plastic surface- some bumps are only 100 atoms high

22. What is friction?
FRICTION- a force that resists motion between 2 surfaces can cause things to heat up- rubbing hands stay still- wax & wood boxes on a ramp slow down- sliding to a stop move- walking

23. 4 TYPES OF FRICTION STATIC friction-
from atoms of each surface attracting each other;
is why it’s tougher to get an object moving than to keep it moving
Demo with logger pro

24. 4 TYPES OF FRICTION SLIDING friction-
from the bumps of each surface getting caught on each other
Start at 4 min

25. 4 TYPES OF FRICTION 3. ROLLING friction- from wheels or bearings
4. FLUID friction-
from motion through a liquid or gas;
Walking/diving in a swimming pool; hand outside of a moving car window; parachute falling
We can change sliding friction into fluid friction if we put a fluid between 2 surfaces

26. Use friction to explain.
MOVING DAY- Do you push harder
to get the table to move or
to keep it going?
Use friction to explain.

27. WHICH WAY?
Friction force is a vector. Which direction does friction push?

28. HOW MUCH?
Friction force is a vector. How much does it push? Speeding up friction force is LESS THAN the pushing force Slowing down friction force is greatest Moving at a constant speed friction force is EQUAL to the pushing force