Transcript force & motion - Boyle County Schools

FORCE & MOTION
Force & Motion
I. Force
A. Def. – a push or pull
B. Measured in Newtons (n) – by a
spring scale
C. Forces in combination
1. same direction 50 N  50N 
= _____N
2. opposite direction 100 N 25 N
= ____ N
D. Friction – force that slows or
prevents motion
1. Sources
a. roughness of surface; ex. road, floor
b. Weight - forces pushing surfaces
together; large object
2. Types
a. static friction – friction at rest; ex.
eraser sits still
b. sliding friction – something pushed
across a surface; ex. box pushed on
floor
c. rolling friction – between wheels
& floor; ex. car
d. fluid friction – friction of liquids
or gases; ex. airplane, boat
3. reducing friction
a. lubricants – oil, wax, grease
b. switch from sliding to rolling
c. smooth surface – ex. use sandpaper
4. increasing friction – make surfaces
rougher & increase the weight (forces
pushing the surfaces together
FRICTION
Why did the teacher insist that her
students wear rain slickers?
She wanted to reduce the friction
between them.
E. Gravitational Force – force of
attraction between any 2 objects
that have mass
1. Law of universal gravitation – all
matter experiences gravity; the size of
the force depends on the masses of the
objects & the distance between them
Alien Song
a. size: sunearthmoon (tides)
b. distance – earth’s gravity affects us
more b/c we are closer
2. weight – measure of gravitational force
F. Centripetal Force – force
which pulls objects toward
the center of a curving path
II. Motion – occurs when an
object changes position over
time
A. Types of Motion
1. neither direction nor speed changes
2. accelerating/decelerating
3. when force applied
4. opposite forces
5. vertical
6. circular
7. projectile
B. Motion described
1. relative position to a reference point; ex.
moving past the middle school
2. Energy- Law of conservation of energy:
energy is neither created nor destroyed;
a. potential – stored energy; ex. car @ top of
hill
b. kinetic – energy in motion; ex. car moving
Kinetic & Potential Energy –
2:56
3. direction – N, S, E, W
4. speed – rate at which object moves
over time
a.) speed = distance/time
ex. 100 miles/2 hrs. = 50 miles/hr
b.) time = distance/speed
ex. 100 miles/ 50 miles/hr = 2 hrs.
c.) distance = speed x time
ex. 50 miles/hr x 2 hrs. = 100 miles
C. Newton’s 3 Laws of Motion
1. Newton’s 1st Law of Motion (Law of
Inertia) – an object at rest or in motion
tends to stay at rest or in motion unless
acted on by a force (INERTIA)
ex.
Seatbelts
Newton’s 1st law of Motion – force, friction, & Inertia –
6:04
2. Newton’s 2nd Law Motion – the
change in motion depends on the mass
of the object & the amount of force
applied;
(a = F/m) OR the amount of force
depends on the mass times the
acceleration
(F = m x a); Ex.
Newton’s 2nd Law –
2:34
3. Newton’s 3rd Law of Motion – for every
force action, there is an equal &
opposite force reaction (actionreaction)
Ex. bike hits car, car hits bike;
Springboard
Newton’s 3rd Law of Motion –
3:00
D. Momentum – measure of how
hard it is to stop an object;
- Law of Conservation of Momentum –
the total momentum of objects that
collide with each other is the same
before & after the collision
THE END!!
bigwheelswreck.mp4