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## Unbalanced (or will it be balanced?) forces exercise

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**Unbalanced (or will it be balanced?) forces exercise**This exercise involves the class being split in two even teams of equal strength outside.**Mass and Weight**Mass – measured in kilograms (kg) this is the amount of matter in an object Weight – (measured in newtons). Weight is the force due to gravity acting on a mass.**Force (measured in Newtons symbol N)**A force is something which can change the motion (speed or direction) of an object. Balanced forces – the object is stationary or at constant speed Unbalanced forces – accelerate,deccelerate or change direction of an object**Finding the weight of an object.**The force due to gravity is 10 Nkg-1 (a constant with symbol g) Force W(N) = mass(kg) x force due to gravity (g) often written as the formula F = mg Work out the weight of a 10Kg bag of potatoes. weight of potatoes = 10kg x 10 N/kg = 100 N**What is the weight of**500g of butter? 2.3kg of cheese? 500mg panadol tablet ? 5 Newtons 23 Newtons 0.0005kg x 10 = 0.005N Task: Working out your weight Use the scales to find your mass in kgs Calculate your weight in newtons using the formula F =mg**Finding the weight of an object on the moon.**The force due to gravity on the moon is 6Nkg-1 Work out the weight of a 10kg bag of potatoes on the moon. weight of potatoes = 10kg x 6 Nkg-1 = 60 N**Exercise – Finding your Force Weight on the Earth and moon**–use the bathroom scales to fill in the table**Starter read page 114 Science to 16**• Write the title force and mass • Write answers to questions on page 115 using full sentences**Force Diagrams**On diagrams forces are drawn with arrows indicating the direction of the force The length of the arrows indicate the strength of the force**Forces acting on an object – you must be able to label**these weight Friction or drag Thrust Friction always opposes motion support When forces are balanced (ie the opposing arrows are the same size)………finish the sentence ..the object is either stationary or moving at a constant speed**Forces acting on an object include**Thrust – makes the object move Friction – opposes motion Weight - pull of gravity Support – upwards push**Force Facts**In the absence of friction a moving object keeps on moving When a force is applied to a stationary object and makes it move, the object gains kinetic energy**Complete cyclist question 6 on sheet – analysing force**diagrams**What causes motion?**• Complete yr 11 yellow workbook page 194**How would you describe and show the unbalanced force acting**on the bike below? Forces can be added or subtracted 4000N 10000N 20000N 4000N Vector arrows are used to show the size and direction of a net force Net force 10000N Acceleration**What is the net downward force?**Describe the motion of the parachutist 1000N 100N 100N Label this force 900N 10N**Friction can be helpful or a nusiance**List areas where friction is helpful List areas where friction is problem**Finding the friction force of different Surfaces – Force**is measured by a force meter in Newtons (N). In this activity we measure the force required to pull blocks with different surfaces over a range of different surfaces Draw this grid in your book**Distance /Time /Speed/Acceleration**Speed is used to describe how fast something is moving Speed is the distance travelled by an object per unit of time**Distance/Time /Speed notes**d = distance (m) t = time (s) v = speed/velocity (ms-1) These are combined in the following equation to give the formula for the average velocity or speed.**d**This triangle can help you to remember the correct formula V t X Task: find the formula for: V = d = t =**The Unit of speed (aka velocity) depends on the units used**to measure distance and time eg The speed limit outside of a school is 50km/hr A snails speed is 4 millimetres per second A world class sprinter runs with a speed of 10 metres per second**The Bugati Vernon has a top speed of 400km/hr**What is its speed in metres per second? To find speed (or V) we need distance in metres and time in seconds Hint convert km to metres and 1 hour to seconds! 1hour = 60minutes and each minute has 60 seconds**The Bugati Vernon has a top speed of 400km/hr**What is its speed in metres per second? 1hour = 60minutes and each minute has 60 seconds So 1 hour = 60min x 60 sec this = 3600s**The Bugati Vernon has a top speed of 400km/hr**What is its speed in metres per second?**find the following**1. What is the speed of a man who walks 300 metres in 120 seconds?**1. What is the speed of a man who walks 300 metres in 120**seconds?**Toy Speeds**Using one car from the front desk measure the speed of it over one metre. Draw the following table in your books. Fill in the distance, time and speed columns making sure you include the correct units.**write this in your book**1. What is the speed of a cyclist who rides 1000 metres in 150 seconds?**write this in your book**1. What is the distance in metres covered by a motorcyclist who rides at 100kmhr-1 for 180 minutes? d = V x t = 100 kmhr-1 x 3hr = 300km = 300000 m**Distance time graphs**Draw the distance time graphs and describe the motion of each object. constant speed Stopped/stationary d (m) d (m) t (s) t (s) Note the greater the slope the faster the speed accelerating Slower constant speed d (m) d (m) t (s) t (s)**c**d b a t Draw the graph A man drives 80 km to Ashburton in 1hour and 10 minutes what is his average speed in m/s? Show all your working and a formula. Copy and complete the following The man had the fastest constant speed at point __ The man got petrol at point ____**Love him or hate him Lance Armstrong is arguably one of the**best cyclists in the world, having won a record 6 Tour de France races. He achieved the record for this race by winning the event 7 times in 2005!! • The first stage of the 92nd Tour de France is • the 19km individual time trial the top two results • are: • Dave Zabriskie (USA ) in 20min 51 sec • 2. Lance Armstrong (USA ) in 20min 53 sec**Questions**What was the average speed (ms-1) of Dave Zabriskie ? Dave Zabriskie (USA ) competed the 19 km in 20min 51 sec Convert kilometers to metres and minutes to seconds 19km = 19000m 19min 51sec = 1251 sec Use formula to find speed**What was Lance Armstrong’s average speed in metres per**second? Lance Armstrong (USA ) completed the 19km in 20min 53 sec**If Lance Armstrong could maintain this speed for one**Hour what distance would he have traveled? (Give your answer in kilometers and metres)**Finding speed from a distance time graph**d 60 50 d (m) P 40 Task Work out the speed for section P 30 K 20 10 T 0 1 2 3 4 5 6 7 8 9 10 t (s)**Finding the average speed of Section P**60 50 d (m) P 40 d T 30 K 20 10 0 1 2 3 4 5 6 7 8 9 10 t (s)**Speed / Time / Acceleration**• V = speed / velocity (ms-1) • t = time (s) • a = acceleration (ms-2) also written as:**∆V**a ∆t X**Calculate the acceleration of a car if changes speed from**20m/s to 50 m/s in 3 seconds**A car travels for 320 kms at 80km/hr how long did it take**him to travel the distance? t = 4 hours**speed / time graphs**Draw the acceleration time / graphs and describe the motion of each object. acceleration constant speed V (ms-1) V (ms-1) t (s) t (s) decceleration or negative acceleration V (ms-1) t (s)**Finding the acceleration from a speed/time graph**Find the acceleration of Section Z 60 50 V (ms-1) V 40 T 30 P 20 10 0 2 4 6 8 10 12 14 16 18 20 t (s)**While playing in the Cricket World Cup, a New Zealand**batsman hit the ball along the ground to the boundary for four runs. The following graph shows the motion of the ball as it rolled along the ground. Distance (m) 1. (a) What was the total distance travelled by the cricket ball? _____________________________________________________(__)m (A) (b) Calculate the average speed of the ball ______________________________________________________________________________________________________________________________________________________________________________________________________average speed =____ms-1 (A)**Force mass and acceleration**When two opposing forces are not equal, they are said to be unbalanced. If an unbalanced force is applied to an object, the object will accelerate. The amount of acceleration depends on the size of the mass and the size of the force. Force mass and acceleration are related by the formula: Where: F = force (N) m = mass (kg) a = acceleration (ms-2) F m a**Example 1**A force of 500N is used to accelerate a 2kg object. What is the acceleration of the object? a = 250 ms -2**Example 2**An object accelerates at 7.5ms-2 when a force of 15000 N is used to accelerate it. What is the mass of the object? m = 2000 kg**While playing in the Cricket World Cup, a New Zealand**batsman hit the ball along the ground to the boundary for four runs. The following graph shows the motion of the ball as it rolled along the ground. Distance (m) 1. (a) What was the total distance travelled by the cricket ball? _____________________________________________________(__)m (A) (b) Calculate the average speed of the ball ______________________________________________________________________________________________________________________________________________________________________________________________________average speed =____ms-1 (A)