What is a force in science? Grade 8 definition and examples

📚 Quick Study Guide

• 🍎 A force is a push or pull upon an object resulting from the object's interaction with another object.
• 📏 Forces are measured in Newtons (N).
• ➡️ Forces have both magnitude (size) and direction, making them vector quantities.
• 🤝 Types of forces include:
  • 💪 Applied Force: A force applied to an object by a person or another object.
  • 🧲 Magnetic Force: The attraction or repulsion between magnetic materials.
  • ⚖️ Gravitational Force: The force of attraction between objects with mass. Near Earth, this is often referred to as weight. $F = mg$ (where $m$ is mass and $g$ is the acceleration due to gravity).
  • friction: A force that opposes motion between surfaces in contact.
• ➕ Net Force: The vector sum of all forces acting on an object. If the net force is zero, the object is in equilibrium.
• Newton's First Law: 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 a force.

Practice Quiz

1. Which of the following is the BEST definition of a force?
   1. A type of energy.
   2. A push or pull.
   3. The mass of an object.
   4. The speed of an object.
2. What unit is used to measure force?
   1. Kilogram (kg)
   2. Meter (m)
   3. Newton (N)
   4. Second (s)
3. Which of the following is an example of a gravitational force?
   1. A car moving down the street.
   2. A ball falling to the ground.
   3. A magnet attracting a metal.
   4. A person pushing a box.
4. What is the net force on an object if two forces are acting on it, one with 10N to the right and another with 5N to the left?
   1. 5N to the right
   2. 5N to the left
   3. 15N to the right
   4. 15N to the left
5. Which of the following is an example of friction?
   1. A rocket launching into space.
   2. A skater gliding on ice.
   3. A book sliding across a table.
   4. A leaf falling from a tree.
6. According to Newton's First Law, what happens to an object in motion if no forces act upon it?
   1. It slows down and eventually stops.
   2. It speeds up.
   3. It changes direction.
   4. It continues moving at the same speed and direction.
7. Which of these is the formula representing gravitational force?
   1. $F = ma$
   2. $E = mc^2$
   3. $F = mg$
   4. $V = IR$