Physics day2

PSHS PHYSICS 3RD YEAR

Session 2

The right tools to succeed in 2nd quarter physics• Know TRIGONOMETRY

Yes, math and physics are very much related!

• Know VECTORS

• Know NEWTON’S LAWS

• Know how to make An FBD (Free Body Diagram)

How to master the tools?

• READ your physics book.

• ANSWER EXERCISES in the book, and verify the answers at the back of the book.

TRIGONOMETRY

• Use SOHCAHTOA

• Set a REFERENCE xy-plane

sinopposite

hypotenuse

cosadjacent

hypotenuse

tanoppositeadjacent

Opposite of what?The REFERENCE ANGLE .

Practice!

A

B

sin cos tanAngle

VECTORS

Operations on vectors• Finding the resultant, given two or more vectors• Finding a missing vector, given the other vectors

and the resultant vector

Method 1: Tail-to-tip(graphical)

Tail of A

Tip of B

Method 2: Parallelogram(graphical also)

Tail-to-tip AND Parallelogram:Which is which?

Parallelogram Tail-to-tip

Subtraction of vectors

• Given a vector A, the negative of A (or –A) is a vector of the same magnitude, but in the opposite direction

Subtraction of vectors

P Q ������������� � P Q

������������� �

Method 3: Component method(computational)

28.056.0A = 44.0

B = 26.5

C = 31.0

Resolve each vector into its x- and y-components

28.056.0

A = 44.0B = 26.5

C = 31.0

VECTOR X-component Y-component

A

B

C

TOTAL

Projectile Motion: The object’s motion has both x- and y-components.

What is the difference between the object’s horizontal (x) component and its vertical (y) component?

y-component:Accelerating downward

x-component:Uniform velocity

Given: an object thrown with a

horizontal velocity

FROM YOUR DIAGNOSTIC:A projectile is fired with an initial speed of 65.2 m/s at an angle of above the horizontal on a long flat firing range. Determine: a) maximum height.

34.534.5

34.5

Formulas you should know:

20 0 0

2 200 0

1 +

2

2 ( )2

xv v v at x x v t at

tv vv

a v v v a x xt

0 0

220

0 0

sin2 1

2

x x y yv v v v gt

vR y y vy t gt

g

c.) the total horizontal distance covered.

FROM YOUR DIAGNOSTIC:A projectile is fired with an initial speed of 65.2 m/s at an angle of above the horizontal on a long flat firing range. Determine: b) total time in the air.

34.5

20 sin2v

Rg

When getting the total time, should we use the equations for the vertical or the horizontal? EITHER will do.

NEWTON’S LAWS OF MOTION

Newton’s First LawLaw of Inertia

Every object continues in its state of rest, or of uniform velocity in a straight line, as long as no net force acts on it.

A school bus comes to a sudden stop, and all the backpacks on the floor start to slide forward. What force causes them to do that? NOT A FORCE. The backpacks continue their

state of motion.

Newton’s Second Law

F = maThe acceleration of an object is

directly proportional to the net force acting on it, and is inversely proportional to its mass.

The direction of the acceleration is in the direction of the net force acting on the object.

What happens when a net force is exerted on a body/object?

Newton’s Third LawAction and Reaction Whenever one object

exerts a force on a second object, the second exerts an equal force in the opposite direction on the first.

Why does a rocket accelerate upward?

RGF

GRF

RG GRF F

Is mass the same as weight?

• Mass – the amount of matter in an object- unit: kilograms

• Weight – gravitational force on an object due to the downward acceleration of gravity. It is always directed downward (direct south).

- unit: Newtons

Object at rest: no NET force acting on it

Exercise: A friend has given you a special gift, a box of mass 10.0 kg. The box is resting on the smooth (frictionless) horizontal surface of a table.

a.) Determine the weight of the box and the normal force exerted on it by the table.

Exercise: A friend has given you a special gift, a box of mass 10.0 kg. The box is resting on the smooth (frictionless) horizontal surface of a table.

b.) Now your friend pushes down on the box with a force of 40.0 N. What is the normal force exerted on the box by the table?

Exercise: A friend has given you a special gift, a box of mass 10.0 kg. The box is resting on the smooth (frictionless) horizontal surface of a table.

c.) If your friend pulls upward on the box with a force of 40.0 N, what now is the normal force exerted on the box by the table?