1. FORCES
Ch 8.1

2. What is FORCE? Recall force is a push or a pull on an object
ELASTIC FORCE
Recall force is a push or a pull on an object
A force can
Move an object
Change the movement of an object
Change the shape of an object
FRICTION FORCE
TENSION FORCE

3. Types of Forces We can group forces into TWO main categories:
(1) Contact Forces
Object is touched
(2) Action-at-a-distance Forces
No touching

4. CONTACT FORCES Contact Force Definition Tension force
A force experienced by a wire or a rope when it’s pulled
Friction force
A force that is caused by two surfaces rubbing together
Elastic force
A force is exerted on a spring-like object and returns to its original shape.

5. Is FORCE Involved???

6. Is FORCE Involved???

7. Is FORCE Involved???

8. Is FORCE Involved???

9. Is FORCE Involved???

10. Is FORCE Involved???

11. Is FORCE Involved???

12. Bigger objects that are close together = greater force
Gravitational Force
2 objects that have MASS are attracted by gravitational force!
Bigger objects that are close together = greater force
We don’t feel gravitational force between ourselves and other objects on Earth because the Earth is so HUGE (it’s gravitational influence is stronger).

13. Electrostatic Force
This is static electricity – caused by CHARGED particles!
Same charges -> repel
Opposite charges -> attract

14. Magnetic Force These forces act on metals (ex: Iron, Nickel...)
Magnets have a field that surrounds them and can exert pushing and pulling forces.
The Earth itself has a natural magnet deep in its core!

16. Freeze High Five What are contact forces? Give 3 examples
What are action at a distance forces? Give 3 examples

17. Mass and Weight Jupiter Mass is the amount of MATTER in an object
Mass is measured in kilograms (kg), use a balance to measure
Weight is different from mass
Weight is the amount of force on an object due to gravity
Gravity is not the same everywhere...
117 kg
50 kg
8 kg
Jupiter
Earth
Moon

18. Measuring Force We measure force in a unit called the newton (N)
1 N is about the amount of force you would need to hold up an apple
1 N
Sir Isaac Newton – handsome fellow
NOTE: Weight is a force so it should be measured in N. We often use kg by habit.

19. Freeze! “High 5” Reading Checks
What units are used to measure a force?
What effect does friction have on the motion of an object?
What is the difference between mass and weight?

20. Forces and Motion Who wins in a tug-of-war? The stronger side!
We can think of forces in this
way!
Forces that are equal and opposite are balanced.

22. Forces and Motion Unbalanced forces causes movement 20 N Net Force
Friction
2 N

23. Unbalanced forces
Four things that could happen to an object if an unbalanced force acts on an object:
Change of speed
Change of direction
It could stop
It start the movement of an object