Types of Force
5 Minutes
Force and resultant force for students: learn how pushes, pulls, balanced forces, and thrusters move objects and spacecraft. An English science lesson.
- How pushing and pulling affects an object under Newton's first law
- Resultant forces and balanced forces shown with arm wrestling
- Like and unlike parallel forces that control spacecraft thrusters
What this lesson teaches
A force is a push or a pull acting on an object, defined by both its numerical value and its direction. When multiple forces act on the same object at once, the combined effect of all these forces is called the resultant force.
How force affects motion
Under Newton's first law of motion, an object will remain at rest or continue moving in uniform motion unless an external force acts upon it. Pushing or pulling an object causes it to move in the same direction as the applied force. Applying force against an object that is already moving can slow it down, bring it to a complete rest, or change its direction entirely. Every force carries a specific numerical value alongside its direction, which determines how strongly and where the target moves.
Balanced and unbalanced forces
- When two or more forces push an object in the exact same direction, those individual forces add together into one larger resultant force.
- If two forces act from opposite directions with equal strength, they create a balanced force, meaning the object does not move at all.
- Arm wrestling illustrates this balanced state when both competitors exert equal force, keeping their hands completely steady in the middle.
- As soon as one person or team exerts a greater amount of force, the balance is lost and the object moves toward the direction of that stronger push.
- The overall direction and movement of any object under multiple forces is always determined by this final resultant force.
Parallel forces in spacecraft
- Scientists in space agencies like the Indian Space Department calculate resultant forces to steer spacecraft and land them smoothly on the Moon or Mars.
- Spacecraft commonly use four booster thrusters to create like parallel forces by firing together in the same direction, propelling the vehicle forward through space.
- Thrusters positioned on opposite sides can fire in opposite directions to slow the spacecraft down, forming what is known as an unlike parallel force system.
- Because these two opposing forces act along parallel lines separated by a distance, they do not cancel each other out into stillness.
- Instead, these unlike parallel forces combine their energy to create a rotational moment, known as torque, which turns the entire spacecraft around its center.