Forces and Newton’s First Law of Motion

8SCIENCE

What is a force?• What happens to an object as it

accelerates?– Speeds up, slows down or turns– There must be some force making it act this

way

• A force is a push or a pull– Examples?– Ex: when you throw a ball, force from your hand moves the ball forward – When the ball hits the ground, the ground produces a force to stop the ball,

maybe making it bounce back up

• Net force is the total force felt by an object– Ex: paper clip held close to a magnet has the force of gravity, and the

magnet’s force being exerted on it

Forces

• Balanced forces cancel each other out – Net force = 0– Do not cause a change in an object’s

motion

• Unbalanced forces – Net force is not 0– The object will accelerate– Ex: friction is an unbalanced force

• Friction is a rubbing force that acts against the direction of motion– Makes objects slow down/stop

Newton’s First Law of Motion

• Newton’s first law of motion states: – An object will remain at rest or move with constant velocity until it

is acted upon by a net force

• What other term related to motionhave we learned that sounds like this?– INERTIA! This is also called Newton’s

law of inertia

• Ex: driving in a car and you are drinking a liquid– The car, yourself and the drink are all travelling at the same speed– If the car suddenly stops you will keep moving, as well as your drink

and it will spill

Friction activityWhat do you observe in these examples with FRICTION? Please write your observations in your SCIENCE JOURNAL and answer the following question for EACH CHALLENGE:a. Which challenge was the most difficult? Easiest? Why do you think so? Explain.

1) Challenge: to drop the coin and the slip of paper from the same height, at the same time, and have the paper and coin reach the ground at the same time

- Take a small piece of paper and make sure it is slightly smaller than the coin- Try and make sure there is as much contact as possible between the coin and paper

2) Challenge: make a card fall perfectly straight. - Drop a playing card with the thin edge downwards (vertical – up and down) - Now try holding the card flat and try to drop it so it moves perfectly straight

Inertia activityWhat do you observe in these examples with inertia? Please write your observations in your SCIENCE JOURNAL and answer the following question for EACH CHALLENGE:

a. Which challenge was the most difficult? Easiest? Why do you think so? Explain.

1) Challenge: Place a card across the top of a cup and place a coin in the middle of the card. Get the coin to drop into the cup by ‘flicking’ the edge of the card in a horizontal direction (side to side) with your index finger.

2) Challenge: Place a card across the top of a cup and place a paper clip on the top of the glass. Repeat step 1 by trying to flick the card so the paper clip goes into the cup.

3) Challenge: Lay a strip of paper over the edge of the cup. Put a coin on the paper strip so that it is balanced on the edge of the cup. Hold the strip of paper with one hand and WITHOUT BREAKING THE PAPER, quickly ‘karate chop’ the strip so it moves out from under the coin but the coin remains balanced.