Forces Pt2 Flashcards
Why will an object always slow down and stop
Friction (if on a solid)
What increases as speed increases
The resistance in a gas or liquid such as air resistance, which works to slow an object down
Can be reduced by making an object more streamlined to allow gas or liquid around it
What do objects falling through gases or liquids reach
Terminal velocity where the velocity reaches its maximum as acceleration gradually decreases
What does terminal velocity depend on
Shape and area, a small area increases the terminal velocity and a parachute for example slows it down
Newton’s first law
A resultant force is needed to make something start moving, speed up or slow down
What happens if the resultant force is the same?
There is a constant velocity
Resultant force equals
Mass times acceleration
Newton’s second law
Force equals mass times acceleration
Inertia
The tendency for an object to remain unchanged
An inertial mass is how difficult it is to change the velocity of an object
Newton’s third law
When a force is applied, an equal and opposite force is returned
Things move because one is lighter
Stopping distance
Thinking distance + braking distance
Thinking distance is affected by
Your speed
Your reaction time
Braking distance is affected by
Speed
Weather or road surface
Condition of tyres
Quality of brakes
How do brakes work?
When the brake pedal is pushed, the brake pads are pressed on to the wheels which causes friction and work to be done and energy is transferred from the kinetic energy store in the wheels to the thermal energy store of the brakes
Faster means more Ke and more work done
Large braking force means large decelerations, breaks can overheat or you skid
Typical reaction time and factors that affect it
0.2 to 0.9 seconds
Tiredness, drugs, alcohol, distractions
Momentum equals
Mass times velocity
Momentum before an event equals
Momentum after an event
Conservation of momentum
Calculate momentum
Equals momentum after
Rearrange to find velocity or mass
What causes a change in momentum
A force
The force changing it is equal to the rate of change of the momentum
Non contact forces
Gravity, magnetism, electrostatic
What to do if the force isn’t the same direction as the movement to find the work done?
Use trigonometry to find the force in the direction of the movement
Then multiply it by distance to find the work done
What other value does the gain in kinetic energy equal?
The loss in gravitational potential energy
If you ignore air resistance
Gain in gravitational potential = loss in kinetic energy
How to find the acceleration if it changes direction?
Make sure that the velocity to the left is a negative value
Work using kinetic energy and gpe
Change in kinetic energy + change in gravitational potential energy
Other power equation
P = F x s
Only if it is moving at a constant speed in the same direction as the power
