Horizontal and vertical motion
Horizontal motion
Projectiles - horizontal motion
The horizontal speed of a An object flying through space unaided by an engine, eg the cannon shot a projectile over the horizon. is constant for the duration of its flight. This is because, once launched, there are no horizontal forces acting on the projectile (air resistance is usually ignored because it is very small) so horizontally the projectile will travel at a When the speed of body does not change, eg the car was travelling at a constant speed of 30 m s-1.. For any calculations involving the projectile's horizontal motion, we use
\(distance = speed \times time\)
\({d} = {v}t\)
Vertical motion
Projectiles - vertical motion
The vertical motion of a projectile is controlled by the force of gravity. This means that there is an When the force in one direction is more than the force in the opposite direction. Eg: With a thrust of 20 N and an opposing frictional force of 15 N, the object experienced an unbalanced force of 5 N in the direction of the 20 N force. Sometimes called the 'resultant force' or 'net force'. acting on the ball and so the ball will accelerate downwards. This acceleration is \(9\cdot 8 ms^{-2}\) (the gravitational field strength on Earth).
As the projectile's vertical speed is not constant, acceleration must be included in any calculation of vertical motion;
\({a_v} = \frac{{{v_v} - {u_v}}}{t}\)
where \(v_{v}\) = final vertical speed and where \(u_{v}\) = initial vertical speed
Sometimes it is more convenient to rearrange the equation to give the The speed of a body after accelerating. Eg: After an acceleration for 5 seconds, the cars final speed was 20 ms -1., vv or Term that describes the order and duration of events. For example, the Physics lesson was 50 minutes long. of flight:
\({v_v} = {u_v} + at\)
or
\(t = \frac{{{v_v} - {u_v}}}{a}\)
The formula for time gives the time of flight of the projectile.
This course will consider projectiles launched horizontally only.
For calculations involving projectiles that are projected horizontally, the following points apply:
- The initial vertical The speed of an object in a particular direction. 'uv' will be zero.
- The acceleration due to gravity 'av' is \(9\cdot\,8\,m\,s^{^{-2}} \).
- If \(t\) can be calculated then Numerical description of how far apart two things are. For example, the distance from Edinburgh to Glasgow is approximately 50 miles. travelled horizontally can be calculated.
Watch this video for a practical demonstration of firing a projectile horizontally and measuring resulting movement and forces.
