GAYA TERPAKSA

Anggaplah selain gaya pemulih dan gaya redaman ada gaya paksa yang bekerja pada benda bermassa  m, kemudian persamaan differensial gerak ini adalah :

 Dengan metode exponensial kompleks, kita selesaikan pertama

Persamaan ini lebih ditulis dalam bilangan kompleks yaitu C dalam bentuk re^iθ. Kita memiliki :

Contoh :

Sebuah pegas vertikal dengan konstanta 48 N/m. pada t  = 0 sebuah gaya diberikan dalam satuan Newton dengan F(t) = 51 sin 4t, t > 0 diterapkan pada benda yang memiliki berat 30 N dalam keadaan seimbang pada ujung pegas. Abaikan redaman, temukan posisi benda pada dalam fungsi t !

Jawab :

                                                      

            Solusi persamaan ini :

                                                y = A cos 4t + B sin 4t – 17/8 cos 4t

           

ketika t = 0, y = 0 dan dy/dt = 0; maka A = 0 dan B = 17/32,

 dan :

                                    y = 17/32 sin 4t – 17/8 cos 4t 

Pembelajaran di Laboratorium Fisika

How  the direction of light change when propagating from air to water ?

Concept :

A transparent material and curved shape can be used as a lens. Light can be refracted when propagating through a different medium.

Materials needed :

·         A transparent vessel containing water

·         Bowl

·         Water

·         Ruler

·         Coin

·         Flashlight

·         Pensil

·         Black paper

Diskusi :

·         What is meant by the lens ?

·         how the lens use ?

·         how light rays are affecting the appearance of objects in the water ?

·         how to change the direction of light rays?

·         how to bend light rays?

Learning Activities :

Part – 1. (This activity is done in pairs)

Hypothesis :

How does the appearance of a pencil partly immersed in a vessel filled with water ?

1.      Put lymph vessel on the table and fill with enough water.

2.      insert a pencil into the water.

   

            Observation :

1.      Observe how the shape of sightings pencil.

2.      How to change the appearance of the form of pencil ?

3.      whether part of the pencil in the water is greater than the parts that do not get into the water?

Part – 2.

Put the bowl on the table and insert a coin into the bowl. Request at some of the learners

to observe coins, furthermore, they have to retreat until the coin invisibles from view.

Hypothesis :

Can coin seen again, if learners do not change its position as the observer and the water is filled into the bowl ?

Designing Experiments :

The other learners must fill the water into the bowl slowly until the coin looks back.

Hypothesis :

whether coin seen more clearly than ever before ?

Application :

How water change the course of the light rays of the coin to the viewer's eye?

Inference :

What conclusions can be drawn based on the two experiments that have been done?

Teacher records :

After doing the activity, the teacher can present the following picture.

Part – 3.

Learners investigate the nature of light propagation using a flashlight, aquarium and other materials. Poposed experimental design with a sketch or charts trial.


sumber :

Ridwan, A. S.2013. Inovasi Pembelajaran. Jakarta : Bumi Aksara.