science (l1 l2 l1)

• Friction is a contact force that exists when one surface slides over another
• Friction is affected by the irregularities in the surfaces of two objects in contact during sliding or rolling
• Friction resists motion and produces heat
• Smooth surfaces provide less friction than rough surfaces
• Types of Friction:

  • Static friction keeps an object at rest until a force greater than the maximum possible static friction is applied
  • Kinetic friction slows down a moving object and can be sliding, rolling, or air friction
  • Sliding friction acts on dry, solid objects sliding on a surface
  • Rolling friction slows down the motion of wheels on a solid surface and is weaker than sliding and static friction
  • Air friction acts on objects moving through the air and is affected by the surface area of the object
• Friction can be increased by increasing the roughness of the surface and decreased by making the surface smooth with lubricants like wax and oil
• Gravity pulls objects toward the center of the Earth and keeps our feet on the ground
• Gravitational force is the only downward force that acts on every object
• One kilogram rock weighs 9.8 newtons on Earth and 1.62 newtons on the moon
• Air friction counteracts gravitational force and decreases the downward speed of a falling object
• Energy is the ability to do work and exists in different forms such as mechanical, sound, heat, radiant, electrical, chemical, and nuclear energy
• Mechanical energy is the energy an object has due to its position or motion and can be potential or kinetic energy
• Potential energy is stored energy possessed by objects at rest, like gravitational potential energy due to an object's position relative to the ground
• Kinetic energy is the energy possessed by objects in motion
• Sound energy is possessed by sound waves
• Thermal energy is possessed by objects due to the movement of particles within them and is released as heat
• Geothermal energy is within the Earth and hydrothermal energy is from bodies of water like the ocean
• Electromagnetic waves carry radiant energy, including light energy visible to human eyes
• Electrical energy is a commonly used form of energy
• Chemical energy is present in food and nuclear energy is stored in the nucleus of an atom and released during nuclear reactions