sciene chap3

• Magnetism


  The force of pushing or pulling between magnetic poles
• Without force, nothing would ever move
• Magnetic Force

  • Acts at a distance and cannot be seen
  • Materials that create this force are magnetic and are called magnets
  • LIKE poles repel, OPPOSITE poles attract
  • Magnetic force is greatest at the poles of magnets
• Gravitational Force

  1. Gravity pulls all objects toward each other

  2. The force of gravity causes objects of different weights to fall at the same time

  3. Gravity between Earth and objects on it is noticeable due to Earth's large mass

  4. Earth's gravity affects the Moon and the Sun's gravity affects Earth
• The size of the mass does not change the rate of speed that objects fall
• Force


  A push or pull that causes an object to move faster or slower, stop, change direction, or change size or shape
• Factors affecting friction


  • Surface texture
  • Amount of surface area
• Rough surfaces


  Have greater friction
• Friction

  The force applied by a surface as an object moves across it
• Frictional Forces

  • Friction is always present when two surfaces rub together
  • Friction can be reduced by using lubricants, making surfaces smoother, or using rollers
  • Friction is affected by surface type and pressure between surfaces
• Smooth surfaces

  Reduce friction
• Greater surface area


  Results in greater friction
• The greater the surface area, the greater the friction
• If tires of a car or truck are larger, more surface area of the tire will touch the road making friction greater
• If more surface of an object touches another object, the friction will be greater
• Trucks have larger tires to make it easier for them to stop or slow down
• Friction


  Soles of shoes have rough textures to increase friction between the shoes and the floor so that it is possible to walk without slipping
• Position


  The position of an object is its location relative to another object (the reference point)
• Lubricants


  A substance put on a surface to reduce friction
• Speed is a measure of the distance an object moves in a certain amount of time
• We use oil in a car to reduce friction on the motor
• Speed is a measure of how fast an object is moving
• Without lubrication, moving parts of machines would slow down or stop very quickly
• Motion


  The motion of an object can be described by its position, direction of movement, and speed
• The distance (length) is the change in position of an object over time when compared with a reference point
• Students should give directions using the terms “north”, “south”, “east”, or “west” shown by the needle of a compass lined up with the direction of the moving object
• Direction of motion can be determined by reading a compass
• Point of reference is your point of view when you observe a motion
• They should also describe the direction of motion by using the terms “right”, or “left” relative to another object, or “up”, or “down” relative to Earth
• The higher the position, the greater the speed and distance will be in the object’s motion
• Speed, ramp height, length, and surface type can affect motion
• Balanced forces are forces equal in size and opposite in direction
• Unbalanced forces cause the object’s motion to speed up, slow down, or stop
• Unbalanced forces occur when one force is greater than its opposite force
• Rate of motion is the speed of the object or how fast or slow the object is moving
• Unbalanced forces

  • Tug-of-war
  • A truck pulling a car
• Unbalanced forces cause a non-moving object to start moving
• Speed is distance divided by time
• Unbalanced forces can cause the speed or the rate of motion to change by increasing, decreasing, or stopping the motion
• The speed of an object is the measure of the distance an object moves in a given amount of time