Types of Forces
Classify contact and non-contact forces and draw force diagrams.
A force is a push or pull that can change an object's shape or motion.
- List common contact and non-contact forces.
- Represent forces with arrows.
- Explain balanced and unbalanced forces.
Contact Forces
Contact forces act only when objects touch:
- Friction — opposes motion between surfaces.
- Normal reaction — the support force from a surface.
- Tension — a pulling force in a rope or string.
- Air resistance — friction from the air.
Non-contact Forces
Non-contact forces act at a distance:
- Gravity — pulls masses together.
- Magnetism — acts between magnets.
- Electrostatic force — acts between charges.
Balanced or Unbalanced
When forces are balanced, the resultant force is zero and motion does not change. When they are unbalanced, the object accelerates in the direction of the larger force.
A book resting on a table has weight acting down and a normal reaction acting up.
The forces are equal and opposite, so the book stays still.
Practice
- Classify as contact or non-contact: gravity, tension, friction, magnetism.
- Draw and label the forces on a box being pushed across a rough floor.
- Explain what happens when a 10 N push is opposed by 6 N of friction.
Recap
Forces are pushes or pulls. Contact forces need touch; non-contact forces act at a distance. Unbalanced forces change motion.
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Forces and Motion
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