Applications of Forces (Use the information on pages 179 – 187)
Application/Diagram
Car Tires
Car Brakes
Electronic Stability Control
Seat Belts
Airbags
Application Description
 rubber is an exception to the relationship between static and
kinetic friction and surface area
 race cars have bigger tires to maximize surface area
 passenger cars have tires with grooves like in the picture to
maintain contact with the road
 In wet conditions if the driver speeds up too much , water
level in front of the tire will increase to the point in which the
tire no longer touches road surface
 Hydroplaning (little to no friction causes driver to lose contact
with the road)
-Car disc brakes are essentially pistons squeezing the brake
pads of the rotor.
-Hard braking increases magnitude of normal force [increases
force of friction] acting upon the rotor which allows you to stop.
-ABS uses a computer to read speed of wheels. If a sudden
increase or decrease in speed occurs the computer quickly
reduces the force on the brake pads.
-problems that may arise from disc brakes could be that the
brakes can stop the wheel from turning a lot faster than the
friction from the road can stop the car from moving. The result
is locked brakes and wheels (sliding can occur); ABS solves this
problem.
-Similar to ABS as the way it is a safety precaution
-Used in cars when the car is speeding up or cornering
-Help maintain full contact on the road
-It uses both traction control and ABS to achieve this
-It monitors the tilt in a car during sharp corners
-When a car doesn't turn enough, it understeers(Figure a)
-If it turn too much, it over steers(Figure b)
-Sensors located in the middle of the car apply one or more
brakes to re-gain control and traction of the car
-However, ESP is only a safety precaution and does not actually
drive the car
2 Safety features
1. Pretensioner
2. Load Limiter
-pulls the seat belt in when
-If too much force is exerted on
the computer detects a crash
the pretensioner...
-keeps person in the optimal
Either
position
-The belt extension will rip
giving
-good for sudden stops and
extra seat belt to slow you
down
mild crashes
OR
-can cause serious injury in
-the locking system will loosen
violent crashes
giving more seatbelt
-counter acts Newton's 1st Law -Stops Newton's 1st Law from
ripping you in half
Air bags are one of the many safety features in cars.
Application/Diagram
Application Description
Airbags expand during car accidents to help prevent people
from roughly smashing into the dashboard/wheel/windshield.
The air bag is folded in the steering wheel/dashboard. They are
sensor activated; which in the event that a collision occurs,
sodium azide reacts with potassium nitrate to create nitrogen
gas. Newton's first law states that objects in motion stay in
motion (inertia), this means that the people in the car will keep
moving forward when the car stops. With the airbag, a person
collides with the air bag instead of the wheel or
windshield/dashboard. As a person collides with the airbag, it
compresses. This reduces the magnitude of force acting on the
person.
Golf Club Design
-The faster you move the head of the club the faster the ball will go
-Swinging harder does not always work
-If the centre of the head does not strike the ball it will travel in the
wrong direction
The Grip- Increases the force of static friction acting on players hands
increasing control
The Shaft- connects grip to head, made of steel or a carbon fibre resin
composite, longer shaft for greater distance, irons have shorter shafts,
more flexible shafts are for players who whip the head to increase
speed
The Head- Direct compact with the ball, heavier head tends to twist
less when hit off centre
Footwear Design (Skates)
µ of the skate blade can be as low as 0.005 when ice is
perfectly smooth.
Physicists thought that this low coefficient was created from
the pressure of the skate on the ice, melting the ice to make it
more slippery. This effect only occurs at 0 degrees Celsius.
It is the slushy layer on the rink that reduces the coefficient of
kinetic friction. The layer is usually very thin (10^-8) and gets
thinner as the ice is cooled. At -25 degrees Celsius, this layer
doesn’t exist and the µ of K of the skate blade on ice is 0.6
Newton's second law is applied through the reduction of weight
in the shoe to increase speed. Also, Newton's Third Law is
applied through the shoe being designed to increase the static
friction exerted by the ground on the athlete. The running shoe
is also designed to counteract increased normal forces which
are caused when athletes impact the ground.
Footwear Design (Running Shoes)
Bearing Design
Bearings are devices that allow surfaces to slide/roll across each
other to help reduce the friction and increase the efficiency of
other devices such as generators. Plain bearings involve 2
surfaces sliding across each other while they are lubricated with
oil or graphite to reduce friction. A ball bearing uses
balls/rollers that are lubricated as well to help reduces the
friction. Fluid bearings use a film of fluid such as oil to separate
2 surfaces. The film reduces the force of friction drastically but
the bearing requires a seal to keep the fluid in and a pump
increase some leaks out. Magnetic bearings use magnetic fields
Application/Diagram
Application Description
to keep 2 surfaces separated. The 2 surfaces do not make direct
contact and so this is often called magnetic levitation. These
bearings require electricity to power the electromagnets. A
backup bearing system is required in case the bearings break.