1. A LEVEL PHYSICS Year 1 Forces in Equilibrium A* A B C
I can explain the effect of balanced forces on an object (Grade D/E)
I can resolve three forces acting on a point. (Grade B)
Understand the conditions needed for a body to be in equilibrium (Grade A)

3. To start Have (from last week)
Calculate the components of the weight of the boy and his sledge parallel and perpendicular to the slope.

4. To start
(from last week)

5. Free-body force diagrams
Shows a single body on its own.
Includes all the forces that act on the body but not the forces it exerts on the rest of the world.
You only need to deal with coplanar forces.

6. From KS3 we should know that... From KS4 we should know that...
Balanced forces
forces
speed
(could be stationary)
Changing speed ( /decelerating)
From KS4 we should know that...
The resultant force of two balanced forces is....
The resultant force of two unbalanced forces is....

7. Draw a free-body force diagram for the following situations.
A tennis ball at rest on court A car moving at constant velocity An object falling at terminal velocity
Draw a free-body force diagram for the following situations.

8. What is equilibrium?
When all forces acting on an object are balanced and cancel out the object is in equilibrium.
When only two forces act, the object is in equilibrium if they are equal and opposite.
Does not have to be stationary to be in equilibrium.
At rest
Moving at a constant velocity

9. What is equilibrium? Have a go at writing a definition...
State of an object when at rest or in uniform motion.
An object is in equilibrium if all the forces acting on it cancel each other out.

10. Force vectors in a closed loop
The forces acting in equilibrium form a closed loop when drawn tip-to-tail – vector polygon.
You won’t ever need to balance more than 3 forces so you only need to worry about vector triangles.

13. Resolving vectors on a slope
(or inclined plane)
Resolving forces on a slope is very useful and will crop up a lot in mechanics. The two perpendicular components of a vector do not affect each other. This means you can deal with the two directions completely separately (when a force only affects one vector you can ignore the other).
Weight always acts vertically down (towards the centre of the earth)

14. Equilibrium Worksheet
Marked for homework

15. To Finish Look at the system that has been set-up It is in equilibrium
Draw a free body force diagram for point P
Show that the resultant of F1 and F2 is equal and opposite to F3

16. Next Lesson: Introduction to Moments
Lesson after that: Advanced Moments