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Force (F) - read text pages 232 , 236 -237
Topics covered – definition of force, units, types of forces, drawing forces acting on an object, effect of a force on an object, contact and non-contact, compare strength of Gravitational force with magnetic, Balanced and Unbalanced forces; Weight and gravity.
Definition : A force is a push or a pull (or a twist) on an object. (vector quantity - i.e. direction is important)
Units - Newtons (N)
Types of forces
Forces can be contact and non-contact.
- Contact forces – exist between objects in direct contact. e.g. push, pull or twist (applied force), friction, tension, normal force, lift, air resistance (drag), upthrust, buoyancy etc...
- Non-contact forces – occur over a distance; there does not need to be direct contact between objects. e.g. Gravitation, Electrostatic, and Magnetic.
- Forces can be either balanced or unbalanced.
Balanced forces
- Do not cause a change in motion.
- Cancel each other out.
- If there are two forces only, they are equal in size and opposite in direction.
- When forces on an object are balanced, the object is either stationary or moving with constant velocity.
Unbalanced forces
- Occur when the forces do not cancel. There is a net unbalanced force (resultant force).
- This will cause a change in the motion of an object. The object will accelerate, decelerate or change direction.
Effect of a force
Balanced forces do not change the motion or shape of an object.
Unbalanced forces effects -
- Depend on the size of force and the mass of object.
- A force can change the motion of an object - start it moving and accelerate it, decelerate and stop it, or change its direction.
- A force can change the shape of an object.
Complete Motion booklet pages 3 - 5 (Questions1- 8) pages 5-7 (Questions 1 - 8)
Text questions Page 237 Ques. 1 - 5, page 238 Ques. 1 - 2
Next page- Gravity and Weight
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