如图所示，在水平的两根筷子中间放上两只乒乓球，通过空心塑料管向两球间用力吹气．可以观察到的现象是_________________，说明的物理原理是__________________。

试题源程序文件清单如下：
//main.cpp
#include＜iostrcam.h＞
class vehicle
private:
int MaxSpeed;
int Weight;
public:
//**********found**********
vehicle(int maxspecd,int weight): (1)
～vehiclc();
int getMaxSpeed()return MaxSpeed;
int getWeight()return Weight;
:
//**********found**********
class hicycle: (2) public vehicle
pnvate:
int Height;
public:
bicycle(int maxspeed ,int weight,int height):vehicle( maxspeed ,weight), Height( height)
int getHeight()return Height;;
;
//**********found**********
class motorcar: (3) public vehicle
private:
int SeatNum:
public:
motorcar( int maxspeed,int weight,int sealnum):vehicle( maxspeed, weight), SeatNum( seatnum)
int getSeatNum()return SeatNum;;
;
//**********found**********
class motorcycle: (4)
public:
motorcycle( int maxspeed ,int weight,int height):
vehicle( maxspeed ,weight), bicycle( maxspeed, weight, height), motorcar( maxspeed, weight,1)
;
void main()
motorcycle a(80,150,100);
cout＜＜a. getMaxSpeed()＜＜endl;
cout＜＜a. getWeight()＜＜endl;
cout＜＜a. getHeight()＜＜endl;
cout＜＜a. getSeatNum()＜＜endl;