To measure and interpret the forces acting on an object in equilibrium.
Forces are pushes and pulled exerted by objects on each other. Contact forces occur when objects are touching. Noncontact forces act from a distance. Gravity is a force of attraction between two objects. The amount of gravitational force depends on the mass of the objects and the distance between them.
When several forces act on an object, the forces combine to act as a single force. The sum of the forces acting on an object is called the net force. When forces act on an object in the same direction, you can find the net force by adding the forces together. When forces act in opposite directions, you must include the direction of the force when you add them. Like numbers on a number line, forces in the direction to the right (or upward) are normally considered to be positive values. Forces to the left (or downward) are negative values. When the net force on an object is 0 (zero) Newtons, the forces acting on it are balanced forces, and the object’s motion does not change. Balanced forces do not affect motion. When the net force acting on an object is not 0 (zero) Newtons, the forces acting on the object are unbalanced forces. Unbalanced forces cause objects to change motion, or accelerate.
Let’s relate this to Newton’s first law of motion, an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
Spring scales (5- or 10-Newton capacity)
2 – 20cm lengths of string
2 table clamps
2 crossbars (short rods)
2 collar hooks
Slotted masses (2 – 200g and 1 – 500g)
Small spirit level