Forces 4

1
Forces (4)
2
More Forces (1)
The force that stops a book falling through a
table or you falling through the floor is the
NORMAL REACTION.
3
More Forces (2)
When an object is in motion, another force to
consider is FRICTION.
This is the resistance to motion from the glass
and the bar scraping together.
4
More Forces Diagrams
When Trev pulls his pet block up a hill. What are
the forces acting on it?
5
A Force Question
Johnny ties his truck to a post to stop it
sliding down the hill. His truck weighs 20N.
What are the values of the forces acting on the
truck?
30o
Step 1 (always) A Force diagram
Because the truck is stationary - - it is in
equilibrium - there is no friction
6
A Force Question (2)
In questions with slopes, it always works out
easiest to resolve forces parallel and
perpendicular to the slope.
R
T
Perpendicular to slope
30o
R 20 cos 30 17.3 N
60o
30o
Parallel to slope
20 N
T 20 sin 30 10 N
7
Activity

• Page ... of your Mechanics 1 book and try
• Q3