Question

How is the motion of an object affected when a force acts on it?
list four types of friction
how does air resistance affect the acceleration of a falling object?
Earth's gravitational force acts in what direction?
describe why a projectile follows a curved path.

Answer 1

1) How is the motion of an object affected when a force acts on it?
- A net force on an object changes its motion by producing an acceleration (Newton’s second law: Fnet = m·a). The acceleration is in the direction of the net force and its magnitude equals the net force divided by the mass. A force can change an object’s speed, its direction of motion, or both. If forces are balanced (net force = 0) the object’s velocity does not change.

2) Four types of friction
- Static friction (prevents start of sliding)
- Kinetic/sliding friction (resists relative sliding motion)
- Rolling friction (resists rolling motion, much smaller than sliding friction)
- Fluid friction (drag in liquids and gases; often called air resistance in air)

3) How does air resistance affect the acceleration of a falling object?
- Air resistance acts upward (opposite the motion) and reduces the net downward force, so the object’s downward acceleration is less than g. As speed increases, drag grows; eventually drag can balance weight and acceleration becomes zero (terminal velocity). The amount of reduction depends on speed, shape, cross-sectional area and air density.

4) Earth's gravitational force acts in what direction?
- Toward the center of the Earth (commonly described as “downward” at the Earth’s surface). Its magnitude near the surface is about g ≈ 9.8 m/s².

5) Why does a projectile follow a curved path?
- The projectile’s motion separates into independent horizontal and vertical components. (Neglecting air resistance) there is no horizontal force so horizontal velocity stays constant; gravity provides a constant downward acceleration that changes the vertical velocity. The combination of constant horizontal speed and steadily changing vertical speed produces a curved (parabolic) trajectory. With air resistance the path is a modified, less symmetric curve.