1. Forces and Angles
Physics 11

2. More bad jokes…

3. Review: Free-body diagrams:
Free-body diagrams are used to show the relative magnitude and direction of all forces acting on an object.
What if some of the forces were not in the x or y plane???????

4. Forces at angles:
We will break the forces with angles into their x and y components using trigonometry!

5. Review: Fnet
Remember we are only worried about Fnet in the direction of the motion
So sometimes we really only need either the x or y component of the force at an angle.

6. Example 1:
You need to move a kg wooden crate across a wooden floor (µ=0.20). You pull with a rope attached at a 15º to the horizontal with a force of 276N.
Calculate the Fapp(X) and Fapp(Y).
What is the acceleration of the crate?

7. a. Fapp(x)= 276 N * cos 15 = (276)(0.9659) = 267 N
Fapp(y)= 276 N * sin 15
= (276)(0.2588)
= 71.4 N
=15º

8. b. Ff = µFN = (0.20)[(25.5)(9.81) = 50.0 N Fnet= Fapp(x) + Ff
FBD
Only need to consider x axis forces as that is the plane of the motion.
Ff = µFN
= (0.20)[(25.5)(9.81)
= 50.0 N
Fnet= Fapp(x) + Ff
= 267N – 50N
= 217 N
Fnet= ma
217= (25.5)a
8.5 m/s2 = a

9. Is it easier to push or pull a sled?

10. Pulling a Sled
A child of 35kg is sitting on a sled that has a coefficient of kinetic friction of 0.10 with the snow. If the parent who is pulling the sled pulls up with an angle of 25°, with what are the component forces?
Draw FBD

11. FBD FN Fa Ff Fg

12. Break Applied Force into ComponentsFa
Fay
Fax

13. Example: Pushing a Sled
A child of 35kg is on a sled that has a µk =0.10 with the snow. If the parent who is pushing the sled pushes down with an angle of 25°, with what are the component forces.
Draw FBD.

14. FBD FN Fa Ff Fg

15. Break Applied Force into Components
Fax
Fay Fa

16. Practice: Force Components: Vectors WS Page 171 #11, 12 (assume no Ff)
Do 5d and 6c together
Page 171 #11, 12 (assume no Ff)
Page 208 # 24, 25