c++ multithreading – trying to make non-const objects const

I have a c++, sfml program and upon trying to implement multi threading have ran into a problem. First off I have little experience with multi threading. When I go to assign the thread tasks it is throwing 22 new errors all relating to objects being const but the objects are not const. Thanks. sorry if the title is poorly worded.

here's some code to look over

class NewKey {
public:
    sf::Image Img;
    sf::Texture Tex;
    sf::Sprite Sprite;
    sf::Vector2i Velocity;
    sf::Vector2i Acceleration;
    sf::Vector2i NextPos;
    bool isMovingLeft() {
        if (Velocity.x < 0)
            return true;
        else
            return false;
    }
    bool isMovingRight() {
        if (Velocity.x > 0)
            return true;
        else
            return false;
    }
    void velocityCap() {
        if (Velocity.x >= 130)
            Velocity.x = 130;
        if (Velocity.y >= 130)
            Velocity.y = 130;
        if (Velocity.x <= -130)
            Velocity.x = -130;
        if (Velocity.y <= -130)
            Velocity.y = -130;
    }
    void loseSpeed(int x) {
        if (isMovingLeft()) {
            Acceleration.x += x;
        }
        else if (isMovingRight())
            Acceleration.x -= x;;
    }
    void StepVelocity() {
        Velocity += Acceleration;
        Acceleration = sf::Vector2i(0, 0);
    }
};

void foo() {
    NewKey Key;
    std::thread thread1;
    std::unique_ptr <sf::RenderWindow> window = std::make_unique<sf::RenderWindow>(sf::VideoMode(100, 100, 32), "Main Window", sf::Style::None);
    Key.NextPos = Gravity(Key, window, thread1);
    thread1.join();
}

sf::Vector2i Gravity(NewKey& Key, std::unique_ptr <sf::RenderWindow>& window, std::thread& thread1) {
    int windSpeed = 2;
    int dropRate = 10;
    thread1 = std::thread([=] {
        if (Key.Velocity.x == 1)
            Key.loseSpeed(1);
        else
            Key.loseSpeed(windSpeed);
        Key.StepVelocity();
        Key.velocityCap();
        if (Key.Velocity.y < 10 && Key.Velocity.y > 0) {
            Key.Velocity.y = 0;
        }
        });
    sf::Vector2i Result = sf::Vector2i(window->getPosition() + Key.Velocity);
    return Result;
}

int main()
{
    foo();
}

the errors

Severity    Code    Description Project File    Line    Suppression State
Error (active)  E1086   the object has type qualifiers that are not compatible with the member function "NewKey::loseSpeed" Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    61  
Error (active)  E1086   the object has type qualifiers that are not compatible with the member function "NewKey::loseSpeed" Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    63  
Error (active)  E1086   the object has type qualifiers that are not compatible with the member function "NewKey::StepVelocity"  Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    64  
Error (active)  E1086   the object has type qualifiers that are not compatible with the member function "NewKey::velocityCap"   Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    65  
Error (active)  E0137   expression must be a modifiable lvalue  Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    67  
Error   C3861   'Gravity': identifier not found Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    53  
Error   C2662   'void NewKey::loseSpeed(int)': cannot convert 'this' pointer from 'const NewKey' to 'NewKey &'  Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    61  
Error   C2662   'void NewKey::loseSpeed(int)': cannot convert 'this' pointer from 'const NewKey' to 'NewKey &'  Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    63  
Error   C2662   'void NewKey::StepVelocity(void)': cannot convert 'this' pointer from 'const NewKey' to 'NewKey &'  Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    64  
Error   C2662   'void NewKey::velocityCap(void)': cannot convert 'this' pointer from 'const NewKey' to 'NewKey &'   Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    65  
Error   C3490   'y' cannot be modified because it is being accessed through a const object  Error   C:\Users\Jacob Krumholz\source\repos\FallingKeys\Error\Error.cpp    67