Today’s Topic

1. Today’s Topic Unit 1: Forces

2. Forces Quantities that have BOTH size and direction are called Vectors. Quantities that have ONLY size are called Scalars.

3. Forces Vectors can be added together in diffferent ways depending on their directions. Vectors moving in the samedirection are ADDED together. Vectors moving in opposite directions are SUBTRACTED from one another. For Vectors moving at right angles to one another, we use the Pythagorean Theorem.

4. Forces A Force is any push or pull. It takes a forceto change an object’s state of motion. The state of motion can be either “at rest” or “moving uniformly in a straight line.”

5. Forces Usually, more than one force acts on an object. The “Vector Sum” of the forces produces a NET FORCE. It is the net force that changes an object’s state of motion.

6. Forces A force diagram (a.k.a. free-body diagram) is a drawing showing all of the forces acting on an object. (FN) (Ff) (Fa) (Fg) or (FW)

7. Forces The force applied is the push or pull on an object. Friction --force between materials that touch. It ALWAYS acts in the opposite direction of the object’s motion.

8. Forces FN—the NORMAL force—is the support force—it balances the object’s weight FW . (FN) If an object is sitting on a horizontal surface, the Normal force must equal the object’s weight. (Ff) (Fa) (Fg) or (FW)

9. Forces • Mechanical equilibrium —state where no changes to the object’s state of motion occur; state of steadiness —NO CHANGE! • ∑F = 0 • Static Equilibrium --objects at rest • Dynamic Equilibrium—objects moving at a constant speed in a straight-line path.

10. Forces From the Force Diagram, it is clear that forces have direction as well as size. (FN) (Ff) (Fa) (Fg) or (FW)

11. Force Diagram for an Incline Normal forces are always perpendicular to the surface of contact. Gravitational forces are always directed straight down towards the surface of the earth.

12. Force Diagram for an Incline

13. Forces Let’s practice finding the vector sum of forces... Practice! Forces are measured in Newtons (N)

14. Four Fundamental Forces • Strong Force: strongest force holding nucleus together • Electromagnetic Force: force existing between charged particles (combination of electric and magnetic forces) • Weak Force: neutrino interaction inducing beta decay • Gravitation Force: weakest force allowing mass to communicate with each other and form relationships

15. Newton’s 1st Law Newton’s 1st Law of Motion restates Galileo’s ideas concerning motion. A body at rest (or in motion) stays at rest (or in motion) unless acted on by an outside force.

16. Newton’s 1st Law Newton’s 1st Law of Motion is also called the Law of Inertia. Inertia is reluctance of any body to change its state of motion.

17. Newton’s 1st Law Mass is the measure of inertia of an object. Mass is also the quantity of matter in an object. More mass = more inertia = more (greater) resistance to change

18. Newton’s 1st Law Mass and Weight are NOT the same. They are proportional to one another. --Massis how much substance there is in an object. Mass is property within the body. --Weightis the force of gravity on an object. Weight is an outside force on the body.