1. The History of Scientific Thought about Forces & Motion

2. Aristotle 384 B.C. – 322 B.C. Greek scientist & philosopher
Made scientific discoveries through careful observations and logical reasoning.

3. Aristotle believed all motion is linear on the planet Earth: meaning everything moves in a straight line. If I throw this rock, it will travel in a straight line, and also fall in a straight line….
                                  
The way Aristotle thought projectiles moved
The way projectiles really move

4. When a feather and rock are dropped at the same time, the rock will fall to the ground first. Aristotle believed that the Earth pulls on objects depending on how much they weigh. This means that a large heavy object will fall to the ground faster than a large light object
        Aristotle Reality      

5. They locked me up for this?
Galileo Galilei
They locked me up for this?
Astronomer & Physicist
Struggled against the church to have his Sun-centered solar system ideas accepted

6. Falling Objects & gravitational pull
Galileo experimented with ramps and dropping things to find that all objects fall at the same rate.
Acceleration due to gravity m/s2 or 9.8 m/s/s

7. Galileo and Constant Acceleration
The inclined plane experiment

8. Galileo’s Projectile experiment http://www. youtube. com/watch

9. Galileo worked out that there was a force acting in the opposite direction to motion and that if this force was decreased (by using oil, grease etc) then the object in motion would move further before stopping. From this Galileo was to formulate his Law of Inertia
Unbalanced Forces!

10. Sir Isaac Newton 1642 - 1727 English mathematician
Built on Galileo’s work

11. The Nature of Force By definition, a Force is a push or a pull.
Just like Velocity & Acceleration, Forces have
both magnitude (size) and direction components.

12. One Newton A Newton (N) is the unit that describes the size
of a force.
One N is equal to
1 kgm/s/s.

13. How Forces Combine More than one force often acts on an object.
When all the forces acting on an object are
added together, you determine the net force
on the object.
An object with a net
force greater than
0 N on it will change
its state of motion.

14. When forces are applied in the same direction, they are added to determine the size of the net force.

15. When two forces act in opposite directions, you subtract the smaller force from the larger force to determine the net force.
The net force will be in the same direction as the larger force.

16. Balanced & Unbalanced Forces
Balanced forces: opposite and equal forces acting on the same object result in NO motion of the object Unbalanced forces – two or more forces of unequal strength or direction acting upon on an object results in the motion of the object

17. 1st Law of Motion
An object will keep the same motion unless acted on by an unbalanced force

18. 2nd Law of Motion
The force of an object depends on the mass of the object multiplied by the acceleration

19. 3rd Law of Motion
Every action force has a equal and opposite reaction force.