Big Ideas
Motion and Forces

An object is moving if its position changes against some background that stays the same. This stationary background is called a reference frame. The change in position in a reference frame is measured in terms of the distance traveled by an object from a fixed point. The distance that an object moves from this reference point per unit of time is called speed. When the direction of motion is included with speed, this is called the velocity of the object. Most objects do not move at a constant velocity through the distance that was traveled. Sometimes there are times of acceleration and deceleration, in which the object is speeding up or slowing down. Acceleration can be calculated by dividing the change in velocity by the time.

A force is a push or a pull that can change an objects velocity (and therefore its acceleration). The net force is the combination of all of the forces acting on an object, which determines whether the velocity of the object will change. When the combination of forces acting on an object combines to produce a net force of zero, the forces are balanced. When the combination of forces acting on an object combines to produce a net nonzero force, the forces are unbalanced.

All objects tend to resist motion; this tendency is called Inertia. An object in motion will remain at a constant velocity unless an unbalanced force acts upon it; in the same regards an object at rest, with zero velocity will remain at zero unless a force causes it to move. Less force is needed to redirect an object that has a low mass than that of an object with a higher mass, which would require a larger force. Therefore, the greater the mass of an object the greater its inertia. Newton’s First Law of Motion is, “An object moving at a constant velocity keeps moving at that velocity unless a net force acts on it. If an object is at rest, it stays at rest unless a net force acts on it.”

Newton’s second law describes the relationship between mass, force and acceleration. The unbalanced force acting on an object equals the object’s mass times its acceleration. We use Newton’s second law to calculate an objects force due to gravity (weight). This is found from the product of an objects mass and the objects free-fall acceleration due to gravity.

For every action, there is an equal and opposite reaction. Newton’s third law state that for every action force, there is an equal and opposite reaction force. These forces always act on different objects. Action/reaction forces never cancel out. They cannot cancel each other out because they act on different objects. The only time forces cancel out (and add up to zero) is when they act on the same object.

  • Heavy objects are harder to move
  • Heavy objects are harder to stop
  • If I turn sharply in my car while driving on ice, I will continue in the same direction
  • I ran a 50 meter dash in 10 seconds.
  • When I pulled a cart with a constant
  • It takes time to move distance.
  • Objects go the direction of a stronger force.
  • Newton ’s First Law of Motion
  • Newton ’s Second Law of Motion
  • Newton ’s Third Law of Motion

  • Speed = Distance/
  • Velocity = Distance /
    Time (With direction)
  • Acceleration =
    Change in velocity/ Time


1. Relate speed to distance and time
2. Distinguish between speed and velocity
3. Calculate the acceleration of an object
4. Describe how forces affects the motion of an object
5. Distinguish between balanced and unbalanced forces
6. State Newton's three laws of motion
7. Explain the differences between mass and weight.

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