TUESDAY 2/16/2016
OPENING:
1) Describe the motion at each segment of this speed/time diagram. A, B, and C.
2) Which segment is acceleration the highest?
KEY TERMS:
INERTIA:
FRICTION:
FORCE:
NET FORCE: Sum of all Forces on an object.
BALANCED FORCES: Net Force=0
UNBALANCED: Net Force does not =0.
Unbalanced force can cause acceleration.
1) Be able to describe the 3 types of FRICTION.
STATIC SLIDING ROLLING
2) What is the direction of the Force of friction?
3) Explain the transformation of energy of friction.
VOCABULARY:
INERTIA: Measure of how hard it is to change an object’s motion; at rest or in motion.
FRICTION: Force in the opposite direction of the motion; slows (decelerates) objects in motion.
FORCE: Push or pull on an object. (N)
NET FORCE: Sum of all the forces on an object.
NEWTON’S 1ST LAW OF MOTION
Net Force (Fnet): the sum of all forces on an object; either balanced (Fnet=0) or unbalanced (Fnetdoes not =0).
IF net Forces are unbalanced: ACCELERATION!
1) IF ‘A’ IS A FORCE OF 10N AND ‘B’ IS A FORCE OF 5N, WHAT IS THE NET HORIZONTAL FORCE?
(Subtract 5N (B) from 10N (A) =5N ß)
ans: Fnet=5 N Left.
(The net force is 5N to the left). The net force does not = 0. UNBALANCED.
The box will be accelerated to the left.
· What downward force is arrow ‘C’ showing? ______
2) What is the net force on a car travelling at a constant speed of 50 mph in a straight line?
Ans: The net force (Fnet) = 0 N.
The net force is zero!
There is no net force on an object that is not accelerating.
NO ACCELERATION: NO NET FORCE!
What Force is the arrow pointing to the Right? ______
3) If there was no friction, how much force would be required to keep an object moving at a constant speed and direction?
______
No force would be required! It would not be accelerating; no acceleration=no net unbalanced force!
So, according to Newton’s 1st Law, the book will stay at rest.
What is the net force on the log?
Which elephant enjoys working more than the other?
CLOSING:
What did you learn about balanced and unbalanced forces on objects today?
Explain in terms of Newton’s 1st Law.
FORCE: N (Newtons) : F=ma
Force=mass x acceleration.
1) What is the Force of a 200kg box accelerated at 5m/s2? ______
2) If F=ma; what does a equal? (solve for a) ______(a=F/m)
3) There has to be contact between two surfaces for the force of friction (they must be touching). What 2 Forces can act at a distance (not touching). ______
4)
NEWTON: (N)Force to accelerate 1kg. 1m/s2.
F=ma
What is the Force of a 1 kg. object
accelerating at 1 meter/sec?
F=1kg x 1m/s2=1N (Newton).
Fnet=sum all the Forces on an object (N)
Fw= weight; the Force of gravity. (N)
Fw=m x a (acceleration due to gravity).
On Earth, the accleration of gravity=9.8m/s.
What is the weight (force due to gravity) of a 100 kg. (mass) man on Earth?
Fw=100kg. x 9.8m/s2=980 N
What would a speed graph of Earth’s acceleration due to gravity look like?
ans.: Straight diagonal line showing constant accleration.
NAME______Date______Per______
Week of 2/16 Goals:
1) Be able to describe the 3 types of FRICTION.
STATIC SLIDING ROLLING
2) What is the direction of the Force of friction?
3) Explain the transformation of energy of friction.
4) Describe and recognize a net unbalanced force.
5) A net balanced force on an object at rest: the object stays at rest. A net balanced force on an object in motion: stays in motion in the same direction and speed.
6) A net unbalanced force in the direction of motion, speeds an object up (accelerates).
7) An unbalanced force in the opposite dirction of motion slows it down (friction is an example).
Helpful exercises:
Balanced/Unbalanced Worksheet
http://www.buckeyevalley.k12.oh.us/userfiles/35/Classes/8577/ForcePractice%202014.pdf
Phet Motion and Forces:
https://phet.colorado.edu/sims/html/forces-and-motion-basics/latest/forces-and-motion-basics_en.html
Self-check Newton’s 1st law
http://glencoe.mheducation.com/sites/0078617707/student_view0/chapter2/section1/self-check_quiz-eng_.html#quest9
Chapter Review quiz
http://glencoe.mheducation.com/sites/0078617707/student_view0/chapter2/chapter_review_quizzes-eng_.html
Preview:
Net unbalanced force of gravity accelerates (changes direction) of the moon. The is called centripedal motion: in a circle or orbit.
Net balanced forces on a floating object. Force A is the force of gravity; Force B is the buoyant force. They are balanced so the object floats