Transcript Thursday Honors PS - elyceum-gamma

Thursday Honors PS
Homework
• Pg 369
• Problems 22-27
Leading Ideas
• Newton’s 1st law
• Newton’s second law
• Weight = mass x 10
(9.8)
Difference between mass and weight
To find the weight of an object
• Weight = mass x acceleration of gravity
• On Earth: acceleration due to gravity is
equal to about 10 (9.8)
Mass and Weight
• Mass:
–
–
–
–
Amount of stuff
Unchanging
Measure of Inertia
kg
• Weight:
– Force of gravity
– Changes because of location
–N
Answers to homework
•
•
•
•
•
•
•
•
22) 10 m/s2
23) 23 N
24) 2.1 kg
25) .04 m/s2
26) 15 N
27) 43.75 N
28) 3.7 N
29) 58.5 N
Additional Problems
• A 2.5 kg hula hoop is pushed forward with
a force of 45.9 N. What is it’s
acceleration?
Answer
• F = ma
• F = 45.9 N
m = 2.5 kg
• A = 45.9 / 2.5 = 18.4 m/s2
Make up a problem
• Object : _______________
• Amount of net force: __________
• Mass of object: ____________
• Solve for acceleration
Example problem
• A 1540 kg car starts from rest and
accelerates to 50.7 m/s in 13.8 seconds.
What is the net force on the car that
causes this acceleration?
Answer
•
•
•
•
1540 kg = mass
Rest = 0 m/s = initial velocity
50.7 m/s = final velocity
13.8 sec = time
• Want net force, but need to find acceleration
a = (vf- vi) / t
a= 3.7 m/s2
then Fnet = ma
Fnet = 5700 N
New homework Handout #3
• Working with Newton’s 2nd Law
• Review conversions, acceleration
• All questions are in book
• Pg 852 3,4
• Pg 857 89-95
• To be handed in on Monday
Newton’s third Law
3rd Law
• For every _____________
There is an __________ but opposite
__________.
• For every action there is an equal and
opposite reaction
• Forces come in pairs
– Equal in size
– Opposite in direction
– Applied to different objects
Examples of 3rd law
Actions that can be related to
rd
3 law in the classroom
If all forces are equal and
opposite, how does anything
move?
Answer
• Though equal in size, the forces act on
different objects
Force of box on ground
Force of ground on
box
Trebuchet
To change the motion of something
• Need to have a net force (unbalanced
forces) on the object in order to change its
motion
Force of rope on box
Friction force
Free Body Diagrams
• Represent the object by a simple
geometric shape or a dot
• Represent all forces on that object by
arrows that originate from shape/dot
• Only represent the forces that are applied
to the object, NOT forces the object
applies to other things
What would be the free body
diagram of …..
• What are the forces
on the dog?
Answer
Reactive
force of
ground
Force of
leash
Applied force of
ground pushing
paws forward
Dog
Weight of
dog
Create a free-body diagram of one
of the dancers
Create a free-body diagram of the
ball
• Draw a free-body
diagram of the rock
climber