Transcript Quantitative FBDs

Quantitative FBDs
Just like in units 1 & 2, our models (x-t, v-t, a-t graphs) didn’t really mean a whole
lot if they couldn’t have predictive power
• Because predictive power requires actual numbers (how fast something will be
going, how far something has traveled) we need to make sure our FBD models
have predictive power as well
With 1-D forces, it’s
fairly easy
5 kg cat sitting
motionless on rug
Fg = 5 kg x 10
Fg = 50 N
m/s2
Fn = 50 N (must
balance Fg)
Fn (R, C)
50 N
50 N
Fg (E, C)
With 2-D forces, we have to do a bit more
work to calculate the forces involved
• Involves basic trigonometry
First, a little intro to basic trig.
Sine, Cosine, and Tangent
•
•
3 main functions in trig
Usually shortened as sin, cos, and tan
To calculate sin, cos, and tan
• Divide the length of one side by
another side……but you must
know which sides!
SOH CAH TOA
Find the height of the flag pole and the hypotenuse
Find the hypotenuse and the length of the side adjacent (next to)
the angle given
Let’s apply what we have just learned to a
more physics-based question:
• An 10 kg object sits motionless on an
incline due to friction
300
The 2000 kg elephant is standing motionless
on the ramp due to friction.
• What is the normal force that the ramp is
pushing up on the elephant with?
What is the force of friction that
prevents the elephant from sliding
down?