弹丸不会以负角向下

Projectile not going downwards on negative angle

我正在构建一个小型物理引擎,它根据用户的一组发射参数(角度、高度、时间间隔和初始速度)发射弹丸,然后显示一些信息,例如总距离或角度它在空中的每个时间间隔:

bool heightCheck = false;
double theta;
double initialVelocity, velocity;
double yNew = 0.0, xNew, xOld = 0.0, yOld = 0.0;
const double time = 0.1;
const double gravitiyHalf = 9.8 / 2;
double velocityX = 0.0, velocityY = 0.0;
double angle = 0.0;
double totalT = 0;
double maxHeight = 0.0;
double thetaDegrees = 0;
#define PI 3.14159265l  // constant for PI

cout << "Insert a lanuch Angle (theta): ";  
cin >> thetaDegrees;    
cout << "Insert a launch height: ";     
cin >> yOld;            
cout << "Insert an initial velocity: ";     
cin >> initialVelocity;     
cout << "Time (DeltaT) in seconds: ";   
cin >> totalT;

for (double deltaTime = 0.0; deltaTime < totalT; deltaTime += 0.1) {

    const double squared = deltaTime * deltaTime;       // squared constant for deltaTime squared

    theta = thetaDegrees * PI / 180;    // converts theta to a degrees value

    velocityX = initialVelocity * cos(theta);   // calculates Vx
    velocityY = initialVelocity * sin(theta);   // calculates Vy

    // apply initialV to velocity
    velocity = initialVelocity + 9.8 * time;

    xNew = xOld + velocity * time;  // works out displacement for X

    yNew = yOld + velocity * deltaTime - gravitiyHalf / 0.5 * (squared);    // calculates Y

    velocityY = velocity - 9.8 * deltaTime; // includes gravity to Y

    angle = atan2(yNew, xNew) * 180 / PI;   // convert angle to degrees

    cout << "\nHeight: " << yNew << endl;
    cout << "Distance in Meters: " << xNew << "m" << endl;
    cout << "Angle: " << angle << endl;
    cout << "Time: " << deltaTime << "s " << endl;

    if (heightCheck == false) {
        maxHeight = yOld;
        // keep maxheight equal to previous height
    }

    if (yNew < yOld && heightCheck == false) {
        heightCheck = true;
        // if projectile is going down, trigger maxheight
    }

    cout << "Maximum height:  " << maxHeight << endl;

    if ((yNew < 0) || (deltaTime == totalT)) {
        getchar();      // stops if delta t = total T or projectile landed
    }

    yOld = yNew;    // refresh x & y
    xOld = xNew;
}

如果我在程序开始时输入以下值:

theteDegrees = 45

yOld = 0

initialVelocity = 20

总计 T = 10

我的程序显示了预期的结果,即我的射弹先升后降。但是,如果我为 thetaDegrees 输入相同的期望值 -40,我的射弹 应该直接向下 ,而不是 它只是上升然后下降.

我的代码哪里出错了?

正如 Igor 所说,在 X 和 Y 的距离计算中,您没有考虑 velocityX 和 velocityY。

    xNew = xOld + velocity * time;  // works out displacement for X
    yNew = yOld + velocity * deltaTime - gravitiyHalf / 0.5 * (squared);    // calculates Y

其中涉及一些冗余计算。更简单的版本可能是这样的。

theta = thetaDegrees * PI / 180;    // converts theta to a degrees value

velocityX = initialVelocity * cos(theta);   // calculates Vx
velocityY = initialVelocity * sin(theta);   // calculates Vy

//cout<<velocityX<<endl<<velocityY<<endl;

for (double deltaTime = 0.0; deltaTime < totalT; deltaTime += 0.1) {

const double squared = deltaTime * deltaTime;       // squared constant for deltaTime squared

xNew = xOld + velocityX * time;  // works out displacement for X

yNew = yOld + velocityY * deltaTime - gravitiyHalf / 0.5 * (squared);    // calculates Y

velocityY = velocityY - 9.8 * deltaTime; // includes gravity to Y

angle = atan2(yNew, xNew) * 180 / PI;   // convert angle to degrees

cout << "\nHeight: " << yNew << endl;
cout << "Distance in Meters: " << xNew << "m" << endl;
cout << "Angle: " << angle << endl;
cout << "Time: " << deltaTime << "s " << endl;

if (heightCheck == false) {
    maxHeight = yOld;
    // keep maxheight equal to previous height
}

if (yNew < yOld && heightCheck == false) {
    heightCheck = true;
    // if projectile is going down, trigger maxheight
}

cout << "Maximum height:  " << maxHeight << endl;

if ((yNew < 0) || (deltaTime == totalT)) {
    getchar();      // stops if delta t = total T or projectile landed
}

yOld = yNew;    // refresh x & y
xOld = xNew;
}

你要么必须改变

xNew = xOld + velocityX * time;  // works out displacement for X

xNew = xOld + velocityX * deltaTime;  // works out displacement for X

或删除

xOld = xNew;

最后,因为两者都保持不变,您将得到二次方加速的 x 坐标,而不是等速的线性运动。