Newton’s 1 st Law. Newton’s First Law of Motion Objects in motion will to stay in motion, objects at rest will stay at rest unless they are acted upon.

Newton’s 1st Law

Newton’s First Law of Motion

• Objects in motion will to stay in motion, objects at rest will stay at rest unless they are acted upon an outside force

• The tendency of matter to maintain its state of motion is known as INERTIA.

Newton’s First Law of Motion

• Inertia prevents an object at rest from moving spontaneously or an object in uniform linear motion from changing its speed or direction spontaneously.

• Force is simply a push or a pull.

Newton’s First Law of Motion

Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless. These pumpkins will not move unless acted on

by an unbalanced force.

Forces

• Usually think of a force as a push or pull• Vector quantity• May be a contact force or a field force

• Contact forces result from physical contact between two objects

• Field forces act between disconnected objects• Also called “action at a distance”

Contact Forces…

• Contact forces are forces which exert a push or pull (interact) while touching.

• Examples:• frictional forces, • tensional forces, • air resistance forces, • applied forces (e.g., pushes or pulls).

Action at a Distance Forces…

• Field Force or Action-at-a-distance forces exert a push or pull (interact) without physical contact.

• Examples:• Gravity (e.g., when you jump off the

ground, there is still a gravitational pull between you and the Earth),

• Electric (e.g., static electricity), • Magnetic (e.g., two magnets).

How Many FUNDAMENTAL Forces?

• Four• Strong Nuclear Force • Electromagnetic Force• Weak Nuclear Force• Gravitational Force

What do they DO?

• Strong Nuclear Force• Holds nucleus together

• Electromagnetic Force• Interaction of electric & magnetic fields

• Weak Nuclear Force• Causes radioactivity

• Gravitational Force• Attracts mass

How Strong are they?

• On a relative scale, we let the strong force = 1, then…

• Strong Nuclear 1.00• Electromagnetic 1 x 10-2 • Weak Nuclear 1 x 10-13

• Gravitational 1 x 10-38

So just how strong is gravity compared to the force that holds the atoms nucleus together?

External and Internal Forces

• External force• Any force that results from the interaction

between the object and its environment• Internal forces

• Forces that originate within the object itself• They cannot change the object’s velocity

Example

When the pellet fired into the spiral tube emerges, which path will it follow? (Neglect gravity).

Example: Answer (b)

When the pellet fired into the spiral tube emerges, which path will it follow and why? (Neglect gravity).

Answer: B Why: Inertia