"Property 'pos' must be a vector" Error when I run VPython Code

Question

When I run this code I get an error "Error: Property 'pos' must be a vector." Do I have to write another vector somewhere? Because I wrote vector at

grav_force = vector(0,-object.mass*grav_field,0)

This is my whole code

GlowScript 2.7 VPython

from visual import *

display(width = 1300, height = 1000)

projectile = sphere(pos = (-5,0,0),
                    radius = 0.1,
                    color = color.red,
                    make_trail = True)

projectile.speed = 3.2 # Initial speed.
projectile.angle = 75*3.141459/180 # Initial angle, from the +x-axis.

projectile.velocity = vector(projectile.speed*cos(projectile.angle),
                             projectile.speed*sin(projectile.angle),
                             0)

projectile.mass = 1.0
grav_field = 1.0

dt = 0.01
time = 0

while (projectile.pos.y >=0):
    rate(100)

    # Calculate the force.
    grav_force = vector(0,-projectile.mass*grav_field,0)

    force = grav_force

    # Update velocity.
    projectile.velocity = projectile.velocity + force/projectile.mass * dt

    # Update position.
    projectile.pos = projectile.pos + projectile.velocity * dt

    # Update time.
    time = time + dt

Answer 1

Change

projectile = sphere(pos = (-5,0,0), radius = 0.1,color = color.red, make_trail = True)

to

projectile = sphere(pos = vector(-5,0,0), radius = 0.1, color = color.red, make_trail = True)

See documentation

http://www.glowscript.org/docs/VPythonDocs/sphere.html

also from documentation

How GlowScript VPython and VPython 7 differ from Classic VPython 6

· Vectors must be represented as vector(x,y,z) or vec(x,y,z), not as (x,y,z).