Forces 2

Pressure You can not wear studded football boots indoor because the damage the floor This is because the studs have a smaller surface area than your foot Pressure is measured in N/m 2

Objects Exerting High Pressure People have been stabbed with high heel (stiletto) shoes Razor blades have a small surface area to exert a lot of pressure Drawing pins have a sharp end that can exert a lot of pressure and stick into boards

Spreading Out Weight Caterpillar tracks spread out the weight of a tank Snow boots prevent people from sinking into the snow

Caterpillar Tracks The t-55 Soviet tank

The Snowcat

Pressure Questions Why does a JCB have caterpillar tracks? To spread it’s weight out and prevent it sinking into mud (Reduce it’s pressure on the ground) If a women has a weight of 60 N and each shoe has a surface area of 10 cm². What pressure does she exert on the ground? She has two feet so her combined surface area is 20cm². Pressure = Force / Area 60÷ 20 = 3 N cm²

A footballer weighs 80 N and he exerts a pressure of 10 N/ cm². What is the surface area of one boot? Area = Force/ Pressure Area = 80 / 10 = 8 cm² ( but this is for both boots) The answer is 4 cm²

The pressure the t-55 tank exerts on the ground is 91,500 N/ m². Each of the tanks caterpillar tracks are 2 m². How much does the tank weight? Force = Pressure x Area Force = 91,500 x 4 (A tank has two tracks) Force = 366,000 N

Speed Speed is measured using this equation: Units are metres/ second (m/s) or kilometres/ hour (km/h)

The Blackbird (SR-71) This stealth plane could travel at speeds of mach 3 Mach 3 means three times faster than the speed of sound It holds the record for the fastest plane (2,193mph) It could travel from London to New York in under 2 hours (An ordinary jet would take 6 hours)

Speed Questions If a sprinter runs 100 m in 10 seconds, what is his speed? 100 ÷ 10 = 10 m/sec If a car is travelling at 60 miles per hour for 3 hours how far does it travel? 60 x 3 = 180 miles If a car is travelling 30 miles per hour and it travels 120 miles how long did the journey take? 120 ÷ 30 = 4 hours

A cheetah can run 460 m in 20 seconds. How fast can it run? 460 ÷ 20 = 23 m/sec Cheetah’s prey on gazelles. A gazelle can run for 14 km in 15 minutes. How fast is the gazelle and can it escape the cheetah? 15 x 60 = 900 seconds 14 km = 14, 000 m 14,000 ÷ 900 = 15.6 m/sec The cheetah will catch the gazelle

Distance/ Time Graphs The gradient (or slope) of the graph tells you the speed of an object In this graph the object is not moving

This graphs shows an object moving at a steady speed

This graph shows an object accelerating (getting faster)

Speed/ Time Graphs These graphs show whether an object is accelerating, decelerating or travelling at a steady speed This is a an object travelling at a steady speed

This is an object accelerating

This is an object decelerating

Questions What is happening in this graph? Two objects are travelling the same distance, but the yellow line is faster

What is happening in this graph? An object is travelling at a steady speed, then it increases to a faster steady speed

What is happening in this graph? An object travels at a steady speed, then stops, then moves off at a faster steady speed

What is happening in this graph? Two objects are accelerating to the same speed, but the yellow one is accelerating quicker

What is happening in this graph? Both objects are decelerating to a stop, but the red line is decelerating faster