Physics - Forces 1: Newtons' Laws and Hooke's Laws

What do forces do to an object?

Alter the shape and size of an object and can also change their speed

Weight

Force acting on a mass due to the effect of a gravitational field

Electric

Attraction or repulsion between two charged objects

Magnetic

Attraction or repulsion due to magnetic fields

Tension

Occurs within materials / objects when stretched e.g. in a spring suspending an object

Compression

Occurs within materials / objects when squashed e.g. a spring

Lift

An upwards force generated by the wing of an aircraft when there is a difference in pressure above and below the wing

Thrust

A force which propels an object forward - usually refers to forward force generated by engines

Friction (including drag)

A force which opposes the motion of an object

Upthrust

The force which enables objects to float due to the displacement of fluid

Contact

A force which occurs whenever an object rests on something else and which always acts at 90 degrees to the surface where it rests

Newton’s 1st law

Every object in motion or stationary will remain that way until a resultant force changes its motion. E.g. a parked car

Newton’s 2nd law

When a non-zero resultant force acts on an object, the it will cause the object to accelerate AND the size of the resultant force is directly proportional to the acceleration it causes. e.g. pushing a trolley down a hill

Newton’s 3rd law

When two objects interact, the forces they exert on each other are equal (magnitude) and opposite (direction). E.g. the earth and the moon

Resultant force =

Bigger force - smaller force

What is friction?

A force that opposes motion

What is the relationship between unbalanced force, mass and acceleration?

Force = mass x acceleration

Weight =

Mass x gravitational field strength

What is the stopping distance of a vehicle made up of?

The thinking distance (reaction time) and the breaking distance

Factors affecting vehicle stopping time

Higher mass, higher speed, icy road conditions, rain, reaction time

Unbalanced speed =

Accelerating or decelerating

Terminal velocity

When the air resistance has increased enough that it and the weight are equal aka the forces are balanced. This is the maximum constant speed

What is the initial linear region of a force-extension graph associated with?

Hooke’s Law

Elastic behaviour

The ability of a material to recover its original shape after the forces causing deformation have been removed

What is the relationship between force, extension and spring constant if an object obeys Hooke’s Law?

Force = spring constant x extension