1. Balanced & Unbalanced Forces
D. Crowley, 2007

2. Balanced & Unbalanced Forces
Friday, April 21, 2017
Balanced & Unbalanced Forces
To be able to represent forces using arrows, and to understand the affects of balanced and unbalanced forces

3. Word search
Using the word search, see if you can identify the key words
Stick your word search into your book!
You have just five minutes, good luck!

4. Balanced forces - stationary / steady speed
Push & Pull Forces
Remember, we use arrows to represent force - the bigger the force, the bigger the arrow is
The arrow points the way the force is acting
The arrows come in pairs, and if the force is balanced (not accelerating) the arrows will be the same size. If the force is unbalanced (accelerating) the arrows will be different lengths…
Balanced forces - stationary / steady speed
Unbalanced forces - acceleration

5. Car moving at a steady speed
Demonstration
Remember a balanced force means there is no change in acceleration - so if an object is stationary, it will remain still, and if it was already moving, it will stay at that constant speed
An unbalanced force means there is a change in acceleration, in the direction of the greater force
Car stationary
(balanced force)
Car moving at a steady speed
(balanced force)
Car accelerating
(unbalanced force)

6. Push & Pull Forces
Have a go at the worksheet - try and identify where the forces are, and represent them with an arrow - think about the arrows direction (up / down / pointing left / pointing right) and the arrows size
Spring (Elastic Force) (pulling up)
Weight (Gravity) (pushing down)

7. Push & Pull Forces
What forces are involved?

8. Push & Pull Forces
What forces are involved?

9. Balanced? What will happen if the cyclist pedals harder?
If the cyclist pedals harder there will be an unbalanced force, and he will begin to accelerate in the direction he is cycling

10. Balanced? What will happen one team pulls harder than the other?
How would you know if the teams were pulling with an equal force?
If the two sides were pulling with an equal (balanced) force, then there would no be a change in their velocity (i.e. both teams would stay where they are)

11. Extra Questions
Most pictures have more than one force affecting them (i.e gravity, reaction + push / pull forces)
If the forces are the same (balanced) the object will stay still or remain at its original speed. If the forces are different (unbalanced) then the object will accelerate in that direction
In picture (b) - with the lady is pushing the shopping trolley with more force (4N), whilst the resistance is less (2N). This means the trolley is accelerating in the direction the lady is pushing
The length of the arrow is longer, because there is an unbalanced force
Friction is a force which slows objects down, e.g. drag, air resistance, the force used in brakes to stop objects

12. Push & Pull Forces What forces are involved? Reaction Reaction
Contact (pull)
Contact (pull)
Contact (pull)
Friction
Contact (pull)
Contact (push)
Elastic
Elastic
Gravity
Gravity
Gravity
Reaction
Reaction
Reaction
Friction
Reaction
Contact (push) + Gravity
Contact (pull)
Contact (pull)
Contact (pull)
Friction
Reaction + Friction
Gravity
Gravity
Gravity
Gravity
Contact (push) + Gravity

13. Push & Pull Forces What forces are involved? Reaction Elastic
Contact (pull)
Reaction
Gravity
Reaction
Reaction
Contact (push)
Contact (push)
Friction
Friction
Gravity
Gravity
Gravity