private TextView textViewPhysicsPDF;
private TextView textViewPhysicsPractiseTesr;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_physics_material);

    textViewPhysicsPDF = (TextView) findViewById(R.id.physicsPDF);


    textViewPhysicsPDF.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            startActivity(new Intent(PhysicsMaterial.this,PhysicsPDF.class));

        }
    });


}