Motion, Forces, and Simple Machines Unit

Week 35Directions1.Prepare your desk for science.

• Science notebook

2.Use voice level 2 (conversation) to discuss this question: “What is a force? What do you know about forces?”

Targets & Warm Up

Targets:• Students will identify contact forces that affect

motion.• Students will demonstrate and describe the way

things move and change motion.

Warm Up: What is a force? What do you know about forces?

Table of Contents

Date Title Page5-28-15 Contact Forces 87

Once you are finished with the Table of Contents, go to page 87 and add the title and date to the top of the page.

Force

Force• Any push or pull that can make an object

move or make a moving object move faster, slow down, stop, or change direction

Force

• Can change both the position and motion of an object

• The size of the change depends on the strength of the push or pull

Contact Forces

Contact forcesForces that must touch an object to affect it

Contact Forces: Applied Force1. Applied ForceForce which is applied to an object by another object.

Contact Forces: Applied Force

What are some other examples of applied forces that you have seen or experienced? Make sure that the force is between two objects!

Contact Forces: Friction

2. Friction• A force that acts when two surfaces rub together• It can slow or stop moving objects or keep

objects from starting to move

Contact Forces: Friction

• The amount of friction between two surfaces depends on:– The object’s surface– How hard the objects press together

Contact Forces: Friction

A. The smooth base of the skis slides smoothly on the snow.

B. The boy on the grass is having difficulty sliding, because the grass is not smooth and his shoes are getting stuck in the grass.

Contact Forces: Friction

• If you push a box of feathers along the floor, it is easy to push.

• If you push a box of books along the floor, it presses against the floor with more force. This causes more friction. The box is harder to push.

Questions to consider

• What are contact forces?• What are some examples of contact forces?

Isaac Newton’s Laws of Motion

An object at rest tends to stay at rest, and an object in motion tends to stay in motion, with the same direction and speed.

The only reason an object will begin to move, change direction, or change speed is because of a force.

Try this…

• Use contact forces to make the ball move• Use contact forces to make the ball…

–Change speed–Change direction–Stop

Try this…

Make the item moveMake the item change speed

Make the item change direction

Make the item stop

Other Types of Contact Forces• Air resistance force: The air

resistance force acts upon objects as they travel through the air.

• Spring force: The spring force is the force exerted by a compressed or stretched spring upon any object which is attached to it.

Other Types of Contact Forces

• Tension force: The tension force is transmitted through a string, rope, or cable.

• Normal (support) force:– If an object is resting upon a

table then the table is applying force upon the object.

– If a person leans against a wall, the wall pushes on the person.

Reflection Questions

• How do contact forces affect motion?• How do things move and change motion?

Targets (Revisited)

• Students will identify contact forces that affect motion.

• Students will demonstrate and describe the way things move and change motion.

Homework

Subject Homework Due DateScience None None

Types of Forces

Do Monday

• Noncontact forces: Forces that affect objects without touching them– Gravity– Magnetism