A proper frame-rate independent* newtonian physics integration:

Vector forces = 0.0f;

// gravity
forces += down * m_gravityConstant; // 9.8m/s/s on earth

// left/right movement
forces += right * m_movementConstant * controlInput; // where input is scaled -1..1

// add other forces in for taste - usual suspects include air resistence
// proportional to the square of velocity, against the direction of movement. 
// this has the effect of capping max speed.

Vector acceleration = forces / m_massConstant; 
m_velocity += acceleration * timeStep;
m_position += velocity * timeStep;

Tweak gravityConstant, movementConstant and massConstant until it feels right. It is an intuitive thing and can take a while to get feeling great.

It's easy to extend the forces vector to add new gameplay - for instance add a force away from any nearby explosion, or towards black holes.

*edit: as long as your frame rate is constant, this technique will produce correct results. However any variance could introduce small mathematical errors that build up over time.

A proper frame-rate independent* newtonian physics integration:

Vector forces = 0.0f;

// gravity
forces += down * m_gravityConstant; // 9.8m/s/s on earth

// left/right movement
forces += right * m_movementConstant * controlInput; // where input is scaled -1..1

// add other forces in for taste - usual suspects include air resistence
// proportional to the square of velocity, against the direction of movement. 
// this has the effect of capping max speed.

Vector acceleration = forces / m_massConstant; 
m_velocity += acceleration * timeStep;
m_position += velocity * timeStep;

Tweak gravityConstant, movementConstant and massConstant until it feels right. It is an intuitive thing and can take a while to get feeling great.

It's easy to extend the forces vector to add new gameplay - for instance add a force away from any nearby explosion, or towards black holes.

*edit: these results will be wrong over time, but may be "good enough" for your fidelity or aptitude. See this link http://lol.zoy.org/blog/2011/12/14/understanding-motion-in-games for more info.

A proper frame-rate independent newtonian physics integration:

Vector forces = 0.0f;

// gravity
forces += down * m_gravityConstant; // 9.8m/s/s on earth

// left/right movement
forces += right * m_movementConstant * controlInput; // where input is scaled -1..1

// add other forces in for taste - usual suspects include air resistence
// proportional to the square of velocity, against the direction of movement. 
// this has the effect of capping max speed.

Vector acceleration = forces / m_massConstant; 
m_velocity += acceleration * timeStep;
m_position += velocity * timeStep;

Tweak gravityConstant, movementConstant and massConstant until it feels right. It is an intuitive thing and can take a while to get feeling great.

It's easy to extend the forces vector to add new gameplay - for instance add a force away from any nearby explosion, or towards black holes.

A proper frame-rate independent* newtonian physics integration:

Vector forces = 0.0f;

// gravity
forces += down * m_gravityConstant; // 9.8m/s/s on earth

// left/right movement
forces += right * m_movementConstant * controlInput; // where input is scaled -1..1

// add other forces in for taste - usual suspects include air resistence
// proportional to the square of velocity, against the direction of movement. 
// this has the effect of capping max speed.

Vector acceleration = forces / m_massConstant; 
m_velocity += acceleration * timeStep;
m_position += velocity * timeStep;

Tweak gravityConstant, movementConstant and massConstant until it feels right. It is an intuitive thing and can take a while to get feeling great.

It's easy to extend the forces vector to add new gameplay - for instance add a force away from any nearby explosion, or towards black holes.

*edit: as long as your frame rate is constant, this technique will produce correct results. However any variance could introduce small mathematical errors that build up over time.