Set position of RelativeLayout in Activity

Good afternoon.

I want to set the position of two RelativeLayout on the screen, but when the user changes the text of TextSwitcher and RelativeLayout to which it belongs increases in size, so the Jump button is moving up and down. down and would like to leave it in the same place. How can I fix this?

Follow the XML:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="br.com.emergencyonline.Introduction" >

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/introduction_emergency_online"
    android:paddingTop="30dp"
    android:layout_gravity="center" />

<RelativeLayout 
    android:id="@+id/rlDescriptions"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_margin="5dp"
    android:padding="50dp"
    android:background="@color/button_material_light">

<TextSwitcher 
    android:id="@+id/tsIntroduction"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center" />

</RelativeLayout>

<RelativeLayout 
    android:id="@+id/rlPular"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:background="@color/background_material_dark">

<Button 
    android:id="@+id/btnPular"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/jump" 
    android:gravity="center"
    android:layout_centerInParent="true"/>

</RelativeLayout> 

</LinearLayout>