1. Forces acting on an object

2. Mass Mass is the amount of material in something, measured in Kg or g.
The mass of an object does not
change, no matter where the object
is.

3. Gravity Large object exert a significant force of
attraction on object close to them. This is
the force of gravity. It has been
measured as 10 Newtons per kg close to
the Earth’s surface.

4. Weight Object on the surface of the Earth have
the ground pushing back against the force
of gravity pulling down. This force from
the ground is the weight of the object and
is exactly equal the force of gravity on the
Object.
Fw=mg

6. Four forces on an airplane
Lift
Drag
Thrust
Weight (gravity)

7. A parachute falling at constant speed
Gravity
Air resistance

8. Thrust (Driving force) Weight
Car moving at constant speed (from left to right)
Thrust (Driving force)
Weight
Support
Drag (friction)
Air resistance (friction)

9. The physics book shows two forces acting upon the book.
The forces on the book balanced.
The physics book shows two forces acting upon the book.
support
gravity

10. Support 500N Gravity 500N The forces on the person are balanced.
50kg person standing still.
Gravity
500N

11. Support 10N Gravity 10N The forces on the person are unbalanced. Drag
The friction between the table and book surfaces exerts a leftward force upon the rightward-moving book.
Drag
20N
Thrust
40N
Gravity 10N

12. Paper-copter Gravity is a force that pulls us
Discussion: Scientific background
Gravity is a force that pulls us
towards the centre of the Earth. 
All forces are measured in
Newtons, named after
Isaac Newton. The weight of
something is the force it feels
being pulled towards the Earth. 
What Newton discovered was that anything with mass pulls
Things towards it with its gravity.

13. When the paper-copter falls, air pushes
(air resistance) up against the blades, bending
them up just a little. When air pushes upward
on the slanted blade, some of that thrust
becomes a sideways, or horizontal push.
Paper-copter does not move side ways
because there are two blades, each getting
the same push, but in opposite directions.
The two opposing forces work together to
cause it to spin.

14. Gravity
Air resistance