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Pushes and pulls Knowledge-Based Study

Physics · Forces & Newton's Laws · Physics · Forces & Interactions

Physics topic explanations on Pushes and pulls.

Study notes

  1. What is a Force?

    In physics, a force is simply an interaction that, when unopposed, can change the motion or shape of an object. At the most fundamental everyday level, forces can be described as either a push or a pull.

    Every time you interact with an object, you are likely exerting one of these two basic actions:

    • Push: Moving an object away from the source of the force (for example, kicking a football, closing a heavy door, or pressing a key on a keyboard).
    • Pull: Moving an object toward the source of the force (for example, opening a drawer, reeling in a fishing line, or towing a cart).

    Forces do not exist in isolation; they always arise from an interaction between at least two objects.

    Key Characteristics of Pushes and Pulls

    Every push or pull has two essential properties:

    • Magnitude: The strength or amount of force applied. A gentle tap exerts a small force, whereas a strong shove exerts a large force. In the International System of Units (SI), force is measured in newtons (N).
    • Direction: The specific path along which the force acts. A push acts forward or away, while a pull acts backward or toward the source.

    Contact vs. Non-Contact Forces

    Many pushes and pulls are contact forces, meaning the interacting bodies must physically touch. Examples include friction, tension in a rope, and normal contact forces.

    However, some pushes and pulls occur without physical contact, known as non-contact forces. For instance:

    • Gravity: A non-contact pull that attracts objects toward the center of the Earth.
    • Magnetism: A magnetic force can act as a pull (attraction between opposite magnetic poles) or a push (repulsion between like magnetic poles).
    • Electrostatic force: Charged particles can pull or push each other across space depending on their charges.

    What Can Pushes and Pulls Do?

    When a push or a pull is applied to an object, it can cause several observable physical changes:

    1. Starting or Stopping Motion: A stationary object remains still until a push or a pull causes it to begin moving. Likewise, a force acting in the opposite direction can bring a moving object to a halt.
    2. Changing Speed: Pushing an object in the same direction it is already moving causes it to accelerate (speed up). Pulling or pushing against its direction of motion causes it to decelerate (slow down).
    3. Changing Direction: A push directed at an angle to a moving object deflects its path, changing its direction of travel without necessarily changing its speed.
    4. Changing Shape: Applying opposing pushes compresses an object (like squeezing a sponge), while opposing pulls stretch an object (like pulling an elastic band).

    Combining Multiple Pushes and Pulls

    Objects rarely experience only one force at a time. Often, multiple pushes and pulls act simultaneously.

    Balanced Forces

    When two or more forces acting on an object are equal in magnitude but opposite in direction, they cancel each other out. The net force is zero.

    • A book resting on a table is pulled downward by gravity and pushed upward by the table's normal contact force.
    • Because these forces are balanced, the object does not accelerate; its state of motion remains unchanged.

    Unbalanced Forces

    When the forces acting on an object do not cancel out, a non-zero net force is present. Unbalanced forces always cause a change in the object's velocity, producing an acceleration in the direction of the net push or pull.