motion and forces

motion and forces

newtons law

Resultant forces will cause acceleration, which can be described and calculated using Newton's laws of motion. Weight is caused by the gravitational effect of a planet attracting an object’s mass.  

According to Newton's first law of motion, an object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero, this means:

• a stationary object stays stationary
• a moving object continues to move at the same velocity (at the same speed and in the same direction)

Examples of objects with uniform motion

Newton's first law can be used to explain the movement of objects travelling with uniform motion (constant velocity). For example, when a car travels at a constant velocity, the driving force from the engine is balanced by the resistive forces such as air resistance and frictional forces in the car's moving parts. The resultant force on the car is zero.

Other examples include:

• a runner at their top speed experiences the same air resistance as their thrust
• an object falling at terminal velocity experiences the same air resistance as its weight

If the forces acting on an object are balanced, the resultant force is zero

Examples of objects with non-uniform motion

Newton's first law can also be used to explain the movement of objects travelling with non-uniform motion. This includes situations when the speed changes, the direction changes, or both change. For example, when a car accelerates, the driving force from the engine is greater than the resistive forces. The resultant force is not zero.

Other examples include:

• at the start of their run, a runner experiences less air resistance than their thrust, so they accelerate
• an object that begins to fall experiences less air resistance than its weight, so it accelerates .  If the forces acting on an object are not balanced, the resultant force is not zero

  Forces on a submarine

  

  The submarine above has both vertical forces and horizontal forces acting on it. The horizontal forces will not affect its vertical movement and the vertical forces will not affect its horizontal movement.

  The horizontal forces are equal in size and opposite in direction. They are balanced, so the horizontal resultant force is zero. This means that there is no horizontal…